PREFACE. vii 



shells cannot always be brought into harmony with those of the animals. Thus^ 

 for instance, the shells of the Fapeiid^ show a great relation to the Mactuibm, 

 while the animals are most closely allied to the Ti:llinid^. Again, the animal 

 of a Lutraria is that of a My a, while the shell in its hinge character is a slightly 

 modified Mactra. The animal of Glauconomya also resembles that of the Myidm, 

 while the shell is a somewhat modified Fetricola. As far as it was possible atten- 

 tion has been paid to the anatomical characters, but these were not allowed 

 altogether to supersede those of the shells. 



In order to facilitate an insight into the systematical arrangement, as here 

 carried out, I append (see p. xv et seq.) a list in which all the divisions down 

 to the genera, and in most cases also to sub-genera, with the typical species of 

 each, are entered. This will form in certain respects a supplement, as the names 

 of typical species have not in all cases been referred to in the text. It will be seen 

 from this list that I have classed all the known Pelecypoda into 10 orders, 46 

 families, and 530 genera, the sub-genera not being specially numbered. How far 

 this arrangement will find approval from Oonchologists further researches must 

 show. 



2. With reference to the second division of the work, previously alluded to, it 

 will be, I think, convenient to the student to find the lists of cretaceous Pelecypoda, 

 lately published, and partially still in progress, by Prof. Pictet in his Pal. Suisse, 

 rendered more complete. I have supplied several omissions in that work, though 

 I have but little doubt that there are many gaps yet to be filled up. My lists 

 must be consulted together with those of Prof. Pictet, for I have not deemed it 

 necessary to swell the record by a repetition of those references to the literature 

 of the subject which are already accurately given in Pictet 's elaborate accounts. 

 The species of only the last few families have been compiled independently of 

 that work. Suggestions regarding the correct generic determination of the 

 cretaceous species, so far as materials, or descriptions and illustrations, admitted, 

 have been embodied in the lists. 



3. The descriptions of the Indian cretaceous species have been framed with 

 those details believed to be necessary for their identification. Iraproved materials 

 will naturally call for additions, but when these were too imperfect for purposes 

 of identification, separate specific names have been omitted; a figure of the spe- 

 cimen was, however, usually given. Some conchological and geological details 

 are noticed in the summary qn the genera;l character of the Indian cretaceous 

 Pelecypoda (see p. 508), 



