GENEEA PENTAMERUS, &c. 369 



OBSERVATIONS ON THE GENERA PENTAMERUS, PENTAMERELLA, STRICKLAN- 

 DINIA, ANASTROPHIA, AMPHIGENIA, RENSSEL^RIA, etc. 



The Genus Pentamerus was proposed by Mr. Sowerbt in 1813, to indi- 

 cate the peculiar internal structure of P. knightii, which is the type of 

 the genus. Dalma5,* objecting to Sowerbt's name, on the ground that the 

 shell was not five-chambered, proposed the name Gypidia as a substitute ; 

 but the latter has not been adopted by naturalists. 



Since that time, much information has been obtained regarding the 

 disposition of the internal parts of the shells of this genus, through the 

 labors of the European palaeontologists de Verneuil, King, Barrande, 

 M'CoY, ScESS, Davidson, Salter and others. In the meantime, however, 

 other species have been referred to the genus, which, having the general 

 external characteristics of Pentamerus, still possess features that render 

 their union with that genus incompatible ; and farther study has shown 

 the necessity of separating them. Among the European forms which are 

 regarded as strictly referable to the genus, are P. knightii ( Sow.), P. vogu- 

 licus (deVer.), P.galeatus (Dalm.), P.sieberi (Von Buch), P. pelagicus (Bar.), 

 and P. optatus (Bar.); while P. oblongus and P. lens have the characteris- 

 tic features of the genus less conspicuous, the exterior being smooth and 

 the form less rotund. Pentamerus liratus and P. microcamerus have a straight 

 hinge-line and distinct area. 



In 1859, Mr. Billings proposed the separation of certain forms from 

 the typical Pentamerus, under the name of Stricklandia ( Stricklan- 

 DiNuf), which he describes as follows : 



GENUS STRICKLANDIA = STRICKLANDINIA (Billings). 



" Generic characters. Shell usually large, elongate oval, transversely oval or 

 " circular, sometimes compressed : valves nearly equal ; a short mesial septum 

 " in tlie interior of the ventral valve supporting a small triangular chamber 



• Petrefacta Succana, in Konigl. Vet. Acad. Handl., 1827. 



t In consequence of the name being preoccupied in botany, Mr. Biixiiras has proposed to change 

 to Stricelandinia. 



[ Paleontology IV.] 47 



