belonging to the Class Palliobranchiata. 27 



pose a new generic nomenclature in several cases where there are 

 already too many synonyms. 



But although this state of things exists, there is every reason 

 for believing, from the progress which fossil conchology has made 

 of late, that it is gradually passing to a termination : thus Pro- 

 fessor Phillips has happily proposed Hypothyris for an extensive 

 division of shells which have long complicated the genus Tere- 

 bratula. Von Buch* and a few others have judiciously restricted 

 Productus to those shells agreeing with the one (P. Martini) 

 which Mr. James Sowerby considered as typical of the genus. 

 M'Coy has succeeded in establishing the genus Martinia for a 

 number of forms that have been successively, but never satisfac- 

 torily placed in Terebratula, Atrypa and Spirifer. Koninck has 

 skilfully cleared up Fischer de Waldheim's genus Chonetes. Ver- 

 neuil, besides considerably advancing our knowledge of every 

 palaeozoic genus of the class, has clearly shown that the Orthises 

 have no congeneric relationship to certain recent and tertiary 

 Terebratulas as supposed by Philippi and others. And J. De C. 

 Sowerby has done much towards unravelling the genus Atrypa. 



In drawing up the remarks contained in this paper, though it 

 is certain that many errors will be committed by myself, yet I 

 hope to contribute something towards elucidating a subject in- 

 volving many difficulties. 



Before proceeding further, it is necessary to state, that as re- 

 gards the nomenclature of the various genera to be alluded to, it 

 is my intention to give preference to those names which are the 

 earliest on record, however much the groups to which they were 

 originally applied have been divided or enlarged, and provided 

 they are not decidedly objectionable : it will therefore be at once 

 understood, that I intend adopting the names Terebratula, Pro- 

 ductus, Spirifer f, Pentamerus, Strophomena, Leptama, Atrypa, 

 Chonetes, &c. in preference to their substitutes Epithyris, Trigo- 

 notreta, Delthyris, Cyrtia, Cleiothyris, Athyris, Leptagonia, &c. 



Having made these preliminary observations, I now proceed to 

 give a synopsis of the various genera composing the class Pallio- 

 branchiata as far as I think is warranted by our present know- 

 ledge of the subject, after which I shall commence with my pro- 

 posed remarks on certain of these genera. 



* Abhancllungen der Kbnigliclicn Akadcmie der Wissenschaften zu Ber- 

 lin, 1841. 



f In the ' Geology of Russia ' (vol. ii. p. 40) M. Verneuil states that M. 

 Fischer had the honour of being the first to separate from the Terebratulas, 

 under the name Choristites, the shells which are now called Spirifers. The 

 genus Spirifer was proposed in 1815, but Choristites docs not appear to have 

 been published prior to 1825. 



