368 



works, are none other than our friend T. paludinceformis, of 

 the Spinatus Zone of Gloucestershire. To this we supplement 

 the T. linctus of Moore, which at first he named T. nudus. 

 As we may conclude from the predominant names mentioned, 

 this gasteropod is found throughout the North West German 

 Middle Lias, and nearly always maintains the same horizon 

 namely that here described as the Spinatus Zone. The remaining 

 univalves are tolerably well known to palaeontology, but exist 

 here in scanty proportion. The Ghemnitzia Blainvillei, Mtjnster, 

 collected here has not the pyritous lustre which those I have 

 found on the Dorsetshire coast possess, and which is generally 

 known by Qitenstedt's name of " Scalaria liassica." Another 

 shell, of which I have several examples, is the Phasianella 

 turbinata, Stoliczka. Of this species the late Dr. F. Stoliczka 

 says in his work, page 77, {TJeber die Gastropoden, &c., der Hierlatr- 

 schichten : Vienna, 1861) that a very similar species is described 

 by Dtjnker, Palseontographia, at page 107, 13, T. 10 f., as 

 Paludina Krausseana, from the Lias of Halberstadt. This 

 little shell often occurs with us in well preserved condition, with 

 the test on, which is an exceptional circumstance. 



(c) ConcMfera. — The mineral character of the sediments exer- 

 cises great influence upon the moUusca generally, and especially 

 upon the lamellibranchiata. In sands such as those under 

 consideration, the marly character is favourable to their growth 

 and development, but only when the bottom is sheltered from 

 tempestuous currents. It is evident, even where sands enjoy a 

 sheltered situation, such as in a bay ; there are seasons when 

 they will be agitated by occasional submarine currents. Our 

 best hydrographers have demonstrated that the sandy deposits 

 of a coast are generally found to be full of small-sized dead 

 bivalves. These are the young that have been unable to exist 

 in the vortex of muddy sand when stirred by exceptionally 

 powerful currents. The condition of the fossil lamellibranchiata 

 fully accords with this supposition. Ostrea cymbium, Harpax 

 Parkinsoni, and Modiola scalprum are all small young specimens. 

 Modiola scalprum only an inch in length ; whilst large robust 

 (xresslya, Pectens and Pholadomya, — the latter from deep sea, — 



