PELECYPODA—PRIONODESMACEA. 



429 



181. P. sinuosa Clarke. (Fig. 559.) Devonic. 



Differs from P. ftagilis in its larger size, sinuous surface and 

 undulated outline. 



Genesee : New York. 



^P^ 



LIII. Honeoyea Clarke. 

 Differs from Lunidicardium in the minute, inflected beak, and 

 the abrupt slope from the sides of the umbo to the hinge line. 

 Anterior to the beak is a byssal 

 notch and posterior to the beak is a 

 similar concave area which contains 

 no such opening between the valves. 

 Surface covered with radiating ribs. 

 Devonic. 



182. H. erinacea Clarke. (Fig. 



560. ) Devonic. 



Subtriangular. Surface marked 

 with 12-15 sharply angular ribs al- 

 ternating with 3 or 4 weak rays. 

 The ridge bounding the posterior 

 hinge area gives off four to six hol- 

 low spines. 



Portage : New York. 



Fig. 560. Honeoyea 

 left valve, X 5 » cardinal 

 another left valve, X 3- 

 Clarke, N. Y. Surv. Mem 



erinacea, 

 view of 

 (After 

 .,6.) 



LIV. Ambonychia Hall (emend Ulrich). 



Equivalve and very inequilateral. Beaks nearly or quite ter- 

 minal. No anterior wing present but a more or less winged pos- 

 terior extremity. Valves ventricose, thin, and tightly closed all 

 around. Surface marked with fine radiating striae crossed by con- 

 centric growth lines and obscure undulations. Two small, oblique 

 cardinal teeth present ; lateral teeth absent. Ligament external. 

 Posterior adductor scar large and bilobed ; no anterior adductor 

 present. Pallial line simple. 



Differs from Clionychia in the more convex valves, the more 

 strongly incurved beaks, the radial striations, and in the posses- 

 sion of a small, lobe-like cavity beneath the beaks where in 

 Clionychia there is a mere thickening of the margins of the 

 valves. 



