DEVONIAN SPECIES. 35 



MOLLUSOA. 

 BEACITIOPODA. 



STPvOPHOMENIDJS. 



Gemas HEMIPRONITES, Pander. 



Hemipronites Chemungensis var. arctosteiata, Courad (sp.). 



Plate 3, fig. 2. 



Strophomena Chemungensis, Courad (1843), Jour. Acad. Nat. Sci. PLilad., VIII, 257, pi. 



14, fig. 12. 

 OrtMsina arctostriata, Hall (1861), Thirteenth Eeport Eegeuts Univ. N. T. on State 



Cab. N. H., 80 ; and (1802) Fifteenth do., 185 and 186, flgs. 1 and 2. 

 Streptorhynchus arctostriatus, Hall (1863), Sixteenth Eeport Regents Univ. N. T. on 



State Cab.-N. H., 62. 

 Streptorhynchus Chemnngensis var. arctostriata, Hall (1867), Palajont. N. Y., IV, 71.* 



Shell small, nearly s.emicircular, rather depressed ; hinge very nearly 

 or quite equaling the greatest breadth; lateral extremities about rectangular; 

 anterior and lateral margins forming together a semicircular curve. Ven- 

 tral valve most convex at the beak, which is only moderately prominent, 

 and a little distorted, but not arched, and seems in the figured specimen to 

 have been broken at the apex in becoming detached froiii some body to 

 vv^hich it had grown ; area comparatively low, nearly flat, and very slightly 

 inclined forward, or ranging nearly at right angles to the plane of the valves; 

 pseudo-deltidium triangular and a little convex ; surface marked by small 

 radiating striae. Dorsal valve unknown. 



Length, 0.31 inch; breadth, 0.4,5 inch; convexity of ventral valve, 0.12 

 inch. 



So far as can be determined from a single specimen of a ventral valve, 



* Professor Hall's latest conclusion on this point is, that Conrad's Strophomena 

 Chemungensis, published in 1843, includes, either as varieties or individual modifica- 

 tions of form, etc., all of the following proposed species, viz., Strophomena bifiircata, 

 Hall, 1843; 8. arctostriata, Hall, 1843; 8. pectinacea. Hall, 1843; Orthis perversa, Hall, 

 1847; OrtMsina arctostriata, Hall, 1860; 0. altcrnata, Hall, 1860; and Orthis inequalis 

 and 0. parvis, Hall, 1858; as well as 8trcptorhyuehiis pandora, Billings, 1860. The 

 names 8. pandora, 8. arctostriata, 8. percersa, and 8. pectinacea, he retains for varie- 

 ties of Mr. Conrad's species (see Pakeont. N. Y., IV, 67-73). 



