70 PALEONTOLOGY OF THE UPPER MISSOURI. 



FAMILY RHYNCHOKELLID^E. 



Shell oval, oblong, subtrigonal or globose, fibrous and impunctate; 

 hinge line curved, and without a proper cardinal area ; dental lamiiue 

 varying with the genera ; supports of oral appendages short and curved, 

 or rarely developed into spiral calcified coils, which are always arranged 

 vertically ; muscular impressions much as in Terebratula. 



Animal, in the living representatives of the family, attached by a 

 muscular peduncle passing through an aperture under the beak of the 

 larger valve ; oral arms fleshy, spiral, flexible, and attached to the small 

 curved processes of the smaller valve, towards the middle of the con- 

 cavity of which the apices of the coils are directed ; mantle not adhering, 

 fringed with a few short setas. 



The shells of the Rhynclionellidce have sometimes much the appearance of some 

 forms of the Terebratulidce, but may be distinguished by the absence of a rounded 

 perforation at the extremity of the beak, by their impunctate structure, and differ- 

 ently formed brachial supports. From the Spiriferidce, some types of which they 

 also resemble in form, they are distinguished by the general absence of calcified 

 spiral appendages, or where they do exist, by the apices of the spires being directed 

 vertically, instead of towards the lateral extremities, &c. 



This family includes the genera Rhynchonella,Eatonia,Camarophoria, Pentamerus, 

 Atrypa, Stenocisma, 1 Ccelosjyira, and probably Porambonites and Camerella. The type 

 for which Leiorhynchus has been proposed, and possibly a few other imperfectly 

 known Palaeozoic genera, may also be found to belong to this family. Only the 

 typical genus is known to have living representatives in our existing seas the 

 other groups being extinct, and, so far as known, confined to the Palaeozoic rocks. 



Genus KHYNCHONELLA, FISHER, 1809. 



Synon. Anomia (sp.), LINN^US, and several early authors. 



Rhynchonella, FISCHER BE WALDHEIM, Mem. Soo. Imp. Mosc. II, 1809, . . . BLAINVILLE, Diet. Sci. Nat. t. 

 XLV, 1827, p. 426. D'OBBIGNY (part), Compt. Rend. XXV, 1847, 268. DAVIDSON, Brit. Foss. Brach. 

 Genl. Int. 1854, 93, and of various other authors. 



Trigoriella, FISCHEE DB WALDHEIM, Mem. Soc. Imp. Mosc. II, 1809 (not DA COSTA, 1778). 



Terebratulites (sp.), SCHLOT. Petref. 1820, 250. 



Hypothyris, PHILLIPS, Palaeozoic Fossils, 1841, 55. KINO, Ann. Mag. Nat. Hist. XVIII, 1846. 



Hemithiris (sp.), D'OBBIOKY, Compt. Rend. XXV, 1847, 268. 



Hemithyris, BBONN, Jahrb. F. Min. 246. 



Acanthothiris, D'ORBioNY, An. Sci. Nat. XIII, 1850, 223. 

 Etym. ;vyxt, a beak. 

 Examp. Terebratula acute, SOWERBY. 



Shell oval or trigonal-subglobose ; with or without a mesial fold and sinus; 

 surface with radiating striae, costae or plications rarely smooth or spinous. Beak 

 of larger valve acute, entire, prominent, and more or less curved ; foramen variable 



1 See note on page 16. 



