UIIACHIOPODA* oiD 



Dulman mistook the shell for a member of that genus. The 

 discovery of internal spires, by Professor Beyrich, shows that it 

 only differs from Rttzia in being impunctate and destitute of 

 hinge-area. Some of the specimens have corresponding depres- 

 sions in the sides of the valves (Fig. 173, p), forming pouchea 

 which do not communicate with the interior. 



Family III. — Ehy:s^chonellid.i:. 



Shell impunctate, oblong, or trigonal, beaked ; hinge-line 

 ciu'ved ; no area ; valves articulated, convex, often sharply 

 plaited; foramen beneath the beak, usually completed by a 



Fig. 174. It. nigricans. 



Ventral. 



Fig. 175. 



Doi"£>al. 



Fig. 174. Dorsal valve with the animal ; «, adductor muscles ; i, intestine. 



Fig. 175. R. psittacea, interiors, s, septum ; /, foramen ; d, deltidium ; t, teeth; t', 

 sockets ; c, oral lameUee ; a, adductor impressions ; r, cardinal ; p, pedicle muscles ; o, 

 ovarian spaces. 



deltidium, sometimes concealed; hinge-teeth supported by 

 dental plates ; hinge-plate deeply divided, supporting oral 

 lamellae, rarely provided with spiral processes ; muscular im- 

 pressions grouped as in Terebratula ; vascular impressions 

 consisting of two principal trunks in each valve, narrow, 

 dichotomising, r.ngular, the principal posterior branches inclos- 

 ing ovarian 3 aces. 



Animal [of Rliynchonella) with elongated spiral arms, directed 

 inwards, towards the concavity of the dorsal valve ; alimentary 

 canal terminating behind the insertion of the adductor in the 

 ventral valve ; mantle not adhering, its margin fringed wit i a 

 few short setse. 



PtHYXcnoNELLA, Fischer. 



Synonyms^ Hypothyris, Phil. Hemithyiis (psittac3aj, 

 D'Orbigny. Acanthothyris (spinosa), D'Orbigny. Cyclothyri t 

 (latissima), M'Coy. Trigonella (part), Fischer (not L. nor D.i 

 Costa). 



