333 PALEONTOLOGY OF NEW-YORK. 



GEXIS RiiYNCIIOI^'ELLA (Fischer, 1809). 



The species Rhynchonella loxia is made the type of this genus by its 

 author. It is only within a recent period that the name has been so 

 extensively applied to nearly all the ovoid or subtrigonal plicated, and 

 some smooth shells of all geological epochs, from Lower Silurian to the 

 most recent formations, and it has been recognized in twtf existing species. 



In the Introduction to the Study of the Brachiopoda (page 95 of the 

 English edition, page 117 of the French edition), Mr. Davidson remarks: 

 " The Genus Rhynchonella is one of the oldest types of animal life, 

 " having been repeated from the Silurian epoch up to the present period : 

 " two species are still found alive." 



I have heretofore accepted the general views of palaeontologists 

 regarding this genus, and have described a number of species under it ; 

 but I have long been satisfied that in making such extensive application 

 of the term Rhynchonella, we were in danger of falling into an error of 

 scarcely less magnitude than that of referring all similar forms, with 

 many others, to the Genus Terebbatula. 



Unfortunately the internal characters of R. loxia do not seem to be 

 known : at least I have not seen them illustrated ; and though cited as 

 the type by Mr. Davidson, and figured upon the plate, it is not enume- 

 rated in his list of eighteen examples. Mr. Woodward gives as types 

 R. acuta, furcellata, spinosa, acuminata, nigrescens and psittacea ; species 

 enumerated in Mr. Davidson's list, but he does not cite R. loxia. 



With the interior structure of the type of the genus unknown, while 

 the parts are illustrated from recent species, or from fossil ones supposed 

 to belong to the genus, we are not likely to make satisfactory progress 

 in the arrangement of the fossils usually referred to it. A careful study 

 of those fossils which have been cited as examples of genera, passing 

 through all the geological stages and still existing, has proved, in some of 

 them at least, that the assumption was not well founded ; and I think 



