120 EOCENE MOLLUSCA. 



the margin slightly reflected. In specimens which have not attained the full size, the 

 bases of the whorls are flattened and sharply angulated at the outer margins. 



This species appears to be well characterised ; it is separated by the striation 

 and the form of the aperture, from the several small fossil species described by 

 Lamarck and by Deshayes. 



Size.— Axis 3-10ths of an inch; diameter not quite 3-20ths. 



Localities. — Sconce and Headon Hill ; apparently, it is very rare. 



I cannot close the present Monograph without noticing certain oviform substances 

 which occur, rather plentifully, in the fresh-water formation at Sconce, as to the nature 

 and origin of which various opinions have been entertained. I have been fortunate 

 enough, however, to obtain lately, specimens which appear to me to remove all doubt 

 on the subject, and to show conclusively that these substances are, in fact, the remains 

 of the eggs of some animal. The condition in which they most usually occur, is that 

 of casts formed of the same material as the rock in which they are imbedded ; they 

 present great regularity of form, and resemble, in every respect, the internal cast of an 

 egg. Occasionally only a hollow space, the impression of the egg, is found without 

 the internal cast, and without the calcareous covering, which has been wholly absorbed; 

 and sometimes, though more rarely, the covering of the egg itself occurs ; but in that 

 case the calcareous matter has always been replaced by carbonate of lime, and in this 

 state the inside is sometimes empty — sometimes it is filled with the matrix. The 

 absorption of the calcareous matter, and its occasional replacement by carbonate of 

 lime, are the conditions in which, as we have already seen, the testaceous remains of 

 Mollusca imbedded in the same formation are frequently found. The hypothesis that 

 these substances are the casts or remains of eggs, appears to me to be the only one 

 by which the different states in which they are found can be satisfactorily explained. 

 Where the egg has been broken, the cavity of the shell has been filled by the fluid 

 matrix, and the internal cast is formed. The eggs may, in some instances, have been 

 broken accidentally; but they appear almost universally to have been broken by the 

 young animal on effecting its escape ; for one end of the casts is free, smooth, and 

 regular in form ; while the other end, apparently broken by the animal, is irregular and 

 connected with the external matrtx. If, on the other hand, the egg has been imbedded 

 unbroken, only the cavity formed by it in the matrix remains ; or if the covering of the 

 egg is found, it is either quite empty, or small globules of the carbonate of lime, by 

 which the shell has been replaced, are found attached to the sides. I assume therefore 

 that the substances in question are the remains of eggs, but of what animals it is more 

 difficult to determine. They are of different sizes, varying in length from 2-10ths of 

 an inch to nearly two inches ; in shape they are oval, rounded equally at both 



