xii PEEPACE. 



I have been led to these remarks solely because I am anxious that the 

 progress which is being made in recent conchology towards a better under- 

 standing of the genera and their development should be heartily supported by 

 the researches of the palaeontologist, but not stopped, or even retarded. The 

 palaeontologist has very often to make certain enquiries, particularly with refer- 

 ence to the strata in which the fossils occur independently of the zoologists, but 

 if true progress in the work is to be attained, the one must utilise the work of the 

 other. 



There cannot be the least doubt that Deshayes has done an enormous ser- 

 vice to fossil conchology by his conservative ideas. Knowing the difl&culties 

 accompanying the examination of fossil shells, often imperfect, he has been eagerly 

 watching over the old Lamarckian genera in order that they may not be split up 

 and then lost for insufficient reasons. The charges which he brought against the 

 classificatory alterations of Schuhmacher, Gray, Swainson, and others, have 

 been almost equally strongly brought forward by him in their favor. Thus, in 1843 

 Deshayes most strenuously argued that only one genus Mesodesma (=. FapUaJ 

 should be accepted in his family Mesodesmidcs, but in 1860 he admits exactly 

 the generic divisions which Gray proposed in that family in 1840. I have little 

 hesitation in thinking that Mr. Deshayes will in 1878 admit much of that which 

 was recorded in 1858 by H. and A. Adams in the '^ Genera," a work with which 

 in 1860 he still found most serious fault. 



There is something unusually unsatisfactory to be noticed in the last edition 



of the Paris fossils. In the review of the various families of the MoUusca it 



appears, as a rule, to be the intention of the author to give a conspectus of the 



genera belonging to each family. This conspectus is, however, evidently left 



incomplete. Many of the generic divisions are there omitted which Deshayes 



has not only accepted, but himself proposed in his works on recent conchology, 



as, for instance, in the British Museum catalogues. It would almost appear that 



Mr. Deshayes believed it as yet unsafe to allow the pateontologist an insight 



into the variety of forms which the studies in recent conchology have revealed. 



I can find hardly any other reason to explain the facts, if the family and generic 



expositions in the 2nd edition of the Paris fossils should be taken as intended to 



supersede former ideas expressed by Deshayes ; and this they certainly do appear 



to aim at. Again, some generic divisions are pointed out by Deshayes in his 



general remarks on the families, but are not accepted in the specific descriptions. 



In other cases the identity of genera (as, for instance, of Unio and AmdontaJ 



