438 Mr. J. E. Gray on the Arrangement of the Brachiopoda. 



Fam. 2. Rhynchonellid^. 



The oral arms are elongate, fleshy, supported at the base by 

 two short, hard, diverging shelly laminae arising from the hinge- 

 margin of the ventral valve. 



They are easily known from the Terehratulidce by the cavity of 

 the shell being without shelly plates, its substance not perforated, 

 and its surface being generally radiately plaited. 



Only one species, T. psittacea, is known in the recent state : 

 its animal has been described by Prof. Owen. 



The family is equivalent to the plaited Tei'ehratula of the elder 

 James Sowerby and Von Buch, the non-perforated Terehratula 

 of Carpenter, the genus Hypothyris of Phillips, and part of the 

 family Terehratulidce of King. 



It contains the genus Rhynchonella of Fischer and D^Orbigny 

 = Hypothyris f Phillips ; Comerophoria, King ; Uncites, Defrance ; 

 ? Trigonoremus, Koenig ; Wiyncora^ Dalman j Pygope, Link ; 

 Delthiridceaj M^Coy ; Pentamerus, Sowerby. 



Order IV. Sarcicobrachia. 



The oral arms fleshy to the base and without any shelly sup- 

 port, the lower valve without any processes on the hinge-margin 

 or disc, or except sometimes a slight medial longitudinal ele- 

 vation. 



Fam. 1. Productidje 



consist entirely of fossil species, some much resembling those of 

 the former family ; but the shells are generally spinose ; they are 

 often attached to marine bodies by the surface of the ventral 

 valve, as the genera Productus, Sow., Stropholosia, King, Chonetes, 

 Fischer, Leptaena and Orthis, Dalman, Strophonema, Rafinesque, 

 and Calceola, Lamk. 



This family comprises Mr. King's Productidce, Strophomenidce 

 and Calceolidcs. 



Fam. 2. Craniad^. 



Nearly allied to the last, but the upper valve is simply conic 

 like a Patella, and the animal is attached by the outer surface of 

 the ventral valve. 



The animal has been figured by Miiller, Poli and others. It 

 includes the recent genus Crania of Retzius, including the Orbi- 

 cula of Lamarck, Criopus of Poli. The lower valve of the only 

 recent species I am acquainted with varies greatly in thickness 

 and form according to the position and habitation of the animal. 

 This family in many particulars is allied to Thecidaada. 



