Monomyaria. Fifteen genera and 106 species are known in the Inferior Oolite, only 13 of which passed up from the Lias. It is important to know those forms which unite the two horizons, especially as so complete a change in the fauna occurred at the close of the Lias and commencement of the Inferior Oolite. This group, as we have seen, was represented in the Lias strata by 18 genera and 114 species in the Lower, 16 genera and 60 species in the Middle, and 13 genera and 32 in the Upper Lias, and 13 of these latter lived on into the more calcareous waters of the Inferior Oolite sea. The connecting species are Avicula inæquivalvis, Gervillia Hartmanni, Hinnites abjectus, H. velatus, Lima bellula, L. electra, L. punctata, Pecten articulatus, P. comatus, P. demissus, Perna rugosa, Pinna fissa, and P. Hartmanni. Six genera and 8 species pass up into the Fuller's Earth, which is fairly developed in the Stroud valley, the Bath area, and parts of Somerset; 12 genera and 33 species connect the Inferior and Great Oolite; and no less than II genera and 18 of the same species range to the Cornbrash. Community of species between the Inferior Oolite and Cornbrash could hardly have occurred in the Yorkshire basin, owing to the broken sequence between the Dogger and the Cornbrashthe Grey or Scarborough Limestone, and the Millepore beds, being the two marine series in the midst of the Estuarine beds. The long-range species are Avicula braamburiensis, A. Münsteri, Gervillia acuta, Hinnites abjectus, Lima duplicata, L. pectiniformis, Ostrea acuminata, O. flabelloides, Pecten annulatus, P. crenatus, P. demissus, P. lens, P. personatus, Perna rugosa, Pinna cuneata, and Placunopsis inæqualis. These 16 species, if not as good witnesses as the rarer forms, show that the conditions were such that only minor physical changes affected the fauna during the intervals of time which occurred between the different horizons or sedimentations. Six genera and 9 species pass to the Kellaways Rock, and 3 genera and 8 species to the Oxford Clay, viz., Avicula inæquivalvis, Lima duplicata, L. pectiniformis, Pecten annulatus, P. crenatus, P. demissus, P. lens, and P. vimineus, all moderately deep-sea forms. The Corallian beds contain 3 of those just quoted, with Placunopsis inæqualis, Ostrea solitaria, and O. flabelloides. The Kimmeridge Clay, through the persistent shells Avicula (monotis) inæquivalvis, Ostrea solitaria, Pecten crenatus, P. articu latus, P. demissus, and P. vimineus, keeps up the connection or continuity; but no species of any Jurassic group passes the Portland beds.

Dimyaria.-Seventy genera and 924 species of this group are known in the whole of the Jurassic rocks, and 47 genera and 236 species occur in the Inferior Oolite. Of these species 28 pass to the Fuller's Earth, 71 to the Great Oolite, 8 to the Forest Marble, 20 to the Cornbrash, 8 to the Kellaways Rock, 2 to the Oxford Clay, and 8 to the Corallian beds. The genera most largely represented are— Astarte with 24 species, Arca 12, Cucullæa 16, Modiola 9, Myacites 11, Mytilus 9, Pholadomya 11, Tancredia 10, Trigonia 34. Thus these 9 genera out of the known 47, and 136 species out of 236, constitute more than one half of the Dimyarian fauna of the Inferior Oolite. Assuming that the species in the above nine prolific genera

would probably have a long range in time, we find that the following in the same genera pass to the Great Oolite-in Astarte 10, Arca 4, Cuculloa only 2, Modiola 5 out of 9, Myacites only 1, Mytilus only 1, Pholadomya 4, Tancredia 5, and Trigonia only 4 out of 34; or 36 species out of the 136 in the above genera are common to the Great and Inferior Oolite.

Gasteropoda. The whole of the Jurassic Gasteropoda number 76 genera and 1005 species; and those of the Inferior Oolite 41 genera and 240 species. Only 6 genera and 6 species are common to the Lias and to the Inferior Oolite, thus a totally new Gasteropod fauna, numbering 234, occurs; and, beyond the fact that 22 genera and 40 species are common to it and the Great Oolite, the species are almost confined to the inferior division. Only one species (Alaria Phillipsii) seems to unite the Fuller's Earth with the Inferior Oolite. The largely represented genera are Alaria with 19 species, Cerithium Chemnitzia 9, Nerinaa 12, Pleurotomaria 47, Trochus 20, Turbo 17. The rarer genera are sparingly represented-Bulla, Ceritella, Cirrus, Crossostoma, Fissurella, Melania, Onustus, Pileolus, Pterocera, Scalaria, Solarium, and Spinigera. Only 3 species pass to the Kellaways Rock, viz., Pleurotomaria granulata, Natica punctura, and Alaria trifida, and only the last species passes to the Oxford Clay; while Turbo funiculatus is the only known form common to the Coral Rag and Inferior Oolite.

10,

Cephalopoda.-Ammonites.—Only 42 species occur in the Inferior Oolite; yet the Lias holds 293 species, 3 of which pass to this horizon Harpoceras concavum, Harpoceras radians, and H. insigne, and only one species of the 42 (Am. fuscus) passes to higher beds. This restriction is remarkable and, on stratigraphical grounds, important. These 42 species occupy the three zones of Murchisonæ, Humphriesianus, and Parkinsoni, these zonal types definitely holding their position or horizons in the Inferior Oolite; and whether the beds are largely developed or not, their succession is everywhere the same throughout Britain and the Continent. No group of the Mollusca is so constant in distribution or so valuable to the stratigraphical geologist; but side by side with the Ammonites we may place the Echinoidea as equivalent in value, and equally reliable stratigraphically. Besides the true Ammonites, one species of Ancyloceras (A. annulatum) occurs in the Inferior Oolite.1

Nautili. The 6 species of Nautili that occur in the Inferior Oolite are all confined to it.

Belemnites. We have stated that 112 species are known in the British Jurassic rocks, but only 16 species occur in the Inferior Oolite; two horizons above this, the Fuller's Earth and Great Oolite, yield only 3 species each; none are known in the Forest Marble and Cornbrash.

1 Ancyloceras annulatum is the only species in the Inferior Oolite; and the Kellaways and Oxford-Clay species, A. calloviense, completes our knowledge of the non-involute forms of the Jurassic Ammonitidæ.

Pelecypoda.

Pisces. Hybodus crassus, Strophodus magnus, S. subreticulatus, and S. tenuis are all that we actually know of the Inferior-Oolite fish. No Pycnodont or Lepidotoid form, as we should almost expect, has ever been obtained from the Inferior Oolite.

Reptilia. Thirty-two genera and 130 species range through the whole Jurassic formation. The Fuller's Earth and Kellaways Rock appear to have none. Thirteen genera and 27 species occur in the Great Oolite, 3 genera and 3 species in the Forest Marble, and one species in the Cornbrash. The Oxford Clay contains 13 species, the Corallian rocks 3, the Kimmeridge Clay 43, and the Portlandian 6 species. We state these now, to show the census of the Reptilia through the Jurassic rocks; individually they will be noticed hereafter.

Mammalia.-None known.

Fuller's Earth.

The Fuller's Earth-This argillaceous deposit forms a transition series between the Inferior and the Great Oolite, and is shown in its entire thickness in the Cotteswold Hills, and in the neighbourhood of Stroud and Bath. It is a variable member of the Jurassic series, the term being applied to a thick deposit of blue and yellow clay (Fuller's Earth), which is opaque, soft, and unctuous. In Somersetshire, its thickness is from 120 to 150 feet, and in Dorsetshire 400 feet; it entirely disappears north of Gloucestershire.1

Fauna. The characteristic fossils are Ostrea acuminata, Pecten vagans, Goniomya literata, Homomya Vezelayi, Ceromya concentrica, C. plicata, Terebratula ornithocephala, T. globata, and Rhynchonella

varians.

Only 51 genera and 110 species occur in this division of the Lower Oolites. Seeing that 35 of the 51 genera and 65 of the 100 species were derived from the Inferior Oolite, and that 80 per cent. of the species occurring are also common to the succeeding Great Oolite, this division has no value, save on physical grounds, and this only over a very limited area; for the Fuller's Earth is by no means universal or even general in its distribution. No Plantæ, Amorphozoa, Crustacea, Nautili, Teuthidæ, or Reptilia occur, i.e., 9 of the 14 classes are unrepresented. The value, therefore, of the Fuller's Earthi as a life-group is almost nil; it is only through the Echinodermata and the Pelecy poda that it has position; and 50 per cent. of these are Inferior Oolite species. The Fuller's Earth is an extremely local formation, the Stroud valley near Gloucester and Bath being the only places where it is extensively developed as a purely argillaceous deposit; in Somersetshire it merges on its strike into a calcareous deposit termed the "Fuller's Earth Rock."

Cœlenterata. Anabacia hemisphærica, Montlivaltia Delabechei, M. tenuilamellosa, and M. Wrightii, are the 4 species known.

1 The Fuller's Earth near Cheltenham is a mere thin band of clay; near Stroud it is 70 feet thick; near Wootton-under-Edge 128 feet; and at and near Bath 150 feet thick.

Echinodermata.-One species only belongs to the Fuller's Earth, viz., Pygurus Michelini, and this ranges up to the Cornbrash. Acrosalenia spinosa, Clypeus Plottii, and Pygurus Michelini pass to the Great Oolite; the same 3 species appear in the Forest Marble, and 2 in the Cornbrash.

Annelida.-Serpula triangulata, S. lævigata, and S. tricarinata occur; the first two pass to the Great Oolite.

Crustacea.-None.

Polyzoa.-Diastopora cricopora, D. oolitica, and Terebellaria ramosissima constitute the Polyzoan fauna. These same species pass to the Great Oolite, in which division there are 16 genera and 31 known forms.

Brachiopoda.-Only 4 genera and 14 species occur. The genus Terebratula has yielded 5 species, Waldheimia 4, and Rhynchonella 1. Pelecypoda (Lamellibranchiata).-Monomyaria.-More than 50 per cent. of this group of the Bivalvia pass up from the Inferior Oolite; for out of the 9 genera and 15 species occurring, 6 genera and 8 species are common to the two formations.

The long-range forms are Avicula echinata, Gervillia acuta, Lima duplicata, L. gibbosa, Ostrea acuminata, O. Sowerbyi, and Pecten vagans. Many species range from the Inferior Oolite to the Corallian beds, but do not appear in this argillaceous series. The Ammonites dwindled from 42 species in the Inferior Oolite to 5, the Gasteropoda from 41 genera and 240 species to one genus and one species (Alaria Phillipsii), and the Pelecy poda from 62 genera and 476 species to 18 genera and 36 species, the Dibranchiate Cephalopoda through the Belemnites from 16 species to 3. This decrease from so prolific a fauna could only be due to physical causes; probably a local deep-sea condition. prevailed at the close of the Inferior Oolite period, and with it took place a corresponding migration of those species fitted to the new condition of things.

Dimyaria. Twenty-two genera and 51 species are known, 28 of which are Inferior Oolite, so that, as in the group Monomyaria, 50 per cent. passed up from the beds below. These are chiefly moderately deep-sea forms, such as Trigonia, Thracia, Pholadomya, Nucula, Myacites, Modiola, Homomya, Cuculla, Anatina, &c. Nineteen genera and 36 species passed to the Great Oolite.

Gasteropoda.-It seems incredible that a subformation standing between two such prolific horizons as the Inferior and the Great Oolite (the former possessing 240 species, and the latter 247) should yield only one species (Alaria Phillipsii) which bridged over the time occupied in the deposition of the Fuller's Earth clays; this form first appeared in the Inferior, and died out in the Great Oolite. Yet 40 species somewhere lived on from the Inferior Oolite during the long epoch, and appeared again in the Great Oolite; such a total removal or local migration of a great group is unparalleled in the British Secondary rocks during any period of their long history.

Cephalopoda.Ammonites.-Am. biflexuosus, Am. discus, Am. fuscus, Am. Herveyi, and Am. viator are the only 5 species known.