Notices of Memoirs— B. G. Bell— St. Erth Beds. 469 



Of these small shells the genera Bissoa and Odostomia are the 

 most plentiful, in species and numbers ; about twenty species of the 

 former (including the Hydrobias) and eighteen of the latter genus 

 are present, some being living inhabitants of the British and Medi- 

 terranean seas, while others appear new to science, and will have to 

 be described. The Troclii are nearly all extinct, three only being 

 Crag and living forms. Of Nassa about eight species are present, 

 Nassa serrata being by far the most common, and is nearly identical 

 with the general form of Nassa reticosa, Sowerby, so plentiful in 

 the coprolite pits of the Boyton district in Suffolk; there are also 

 other well-known Crag species of this family. 



The carnivorous Gasteropods are, however, not otherwise plentiful ; 

 one shovild be noticed, a large fragment of Buccinum undatum, but 

 no traces of Fusus antiquus or F. gracilis ; all the Pleurotomas are 

 scarce except P. hracliystoma, and there ai'e two species of JPisania or 

 Lachesis ; all these last are southern forms. 



Of the bivalves not much can be said ; few species were obtained, 

 and these mostly in a fragmentary condition. It is still a difficulty 

 to afford an adequate explanation of this fact, for while the deposit 

 of clay is so well calculated to preserve the shells, as shown by the 

 perfect state of the univalves, the bivalves (if we except the oysters 

 and some minute species) have universally suffered. Some explana- 

 tion other than that of the physical character of the deposit must 

 be sought for, and none has yet appeared sufficiently satisfying. 



The opinion expressed in the earlier reports upon this deposit, as 

 to the southern facies of its fauna, has been amply justified by fresh 

 researches ; a large quantity of the fossiliferous clay has been care- 

 fully washed and examined, and no trace of northern forms, except 

 Buccinum undatum, and the two small species noticed in the paper 

 previously referred to, has been found, while greatly increased 

 evidence confirming what has been already said is present. Had 

 there been any connection with northern seas or colder waters, it 

 would be difficult to understand the entire absence of those forms of 

 Pleurotoma (Bela) so abundant in the Boreal seas of the Crag period 

 and the present age, as well as the equally characteristic bivalves, 

 Astarte and Cyprina. 



Some conflict of opinion exists upon the depth of water in which 

 the St. Erth clays were deposited. 



In a letter to "Nature," of August 12, 1886, a very competent 

 authority on Pliocene phenomena, Mr. Clement Eeid, F.G.S., gave it 

 as at least forty or fifty fathoms, founding his view on the evident 

 fact of its deposition in still water, which he maintains could not be 

 found in a district exposed to Atlantic swells at less depth. To this 

 the writer must take serious exception. Undoubtedly the clays 

 exhibit an entire absence of such a disturbing cause as the influence 

 of great wave action, but it remains to be proved that such a great 

 depression as Mr. Reid describes did occur at the western end of 

 Cornwall, and as far as I have been able to observe there is little 

 indication of such a fact. Some depi'ession, of course, must have 

 happened, sufficient to submerge the low-lying land near St. Erth, 



