160 TWENTIETH KEPORT ON THE STATE CABINET. 



The Genus Leiorhynchus is retained for such forms as L. limit aris 

 and jL. g-z^tti^Wco^^afa, which present, among other distinguishing features, a 

 division or bifurcation of the plications on the mesial fold and sinus. The 

 species recognized as belonging to this genus are X. limitaris, L. mysia (n. s.), 

 L. quadricostata, L. 7nulticosta, L. iris ( n. s.), L. kelloggi (n. s.), L. sinua- 

 tus (n. s.), L. mesacostalis, L. globuliformis, L. dubius (n. s.). 



Under the Genus Leptoc(ELIA, the L, acutiplicata is the only species 

 recognized. 



The Genus Camarophoria has been observed in a single smooth spe 

 cies, the C eucharis, from the Upper Helderberg limestones. 



Some of the pentameroid forms, heretofore referred to the Genus Pen- 

 TAMERUS, are placed under new genera, on account of certain peculiarities 

 of their internal structure. The reasons for this course are given in the fol- 

 lowing observations on the Genera Pentamerus, Pentamerella, etc. 



OBSERYATIONS ON THE GENERA PENTAMERUS, PENTAMERELLA, 

 STRICKLANDINIA, ANASTROPHIA, AMPHIGENIA, RENSSEL^RIA, 

 etc. 



The Genus Pentamerus was proposed by Mr. Sowerby in 1813, to 

 indicate the peculiar internal structure of P. Jcnightii, which is the type of 

 the genus. Dalman*, objecting to 8owerby'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 dis- 

 position of the internal parts of the shells of this genus, through the labors 

 of the European palaeontologists de Yerneuil, King, Barrande, M'Coy, 

 SuEss, 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 regar- 

 ded as strictly referable to the genus, are P. knightii ( Sow.), P.vogulicus 

 (de Yer.), p. galeatus (Dalm.), P.sieberi ^Yon Buch), P. pelagicm 

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

 characteristic 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 (Strick- 

 landiniaI), 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 



* Petrefacta Suecana, in Konigl. Vet. Acad. Handl., 1827. 



t In consequence of the name being preoccupied in botany, Mr. Billings has propc^tftd to change 

 to Stkxcklandinia. 



