FOSSILS OF THE HUDSON EIVER GROUP. 81 



on top, 0X1 others they are rounded, the spaces between being very nar- 

 row, or even wider than the ribs — the surface may be smooth or con- 

 centrically striated ; yet among all these features there are none constant 

 enough to constitute specific distinctions. Among specimens of A. radi- 

 ata from the same rocks in New York, we find corresponding differences. 

 The species A. radiata was founded upon the finely radiated forms, while 

 the more coarsely ribbed form, which is sometimes quite angular on the 

 umbonal ridge, was identified with Pterinea carinata, Goldf., which was 

 originally described from a specimen of this character from New York, 

 and which agrees, in most respects at least, with the western form known 

 as Ambonychia cosfata, James. 



Formation and locality: In the higher beds of the Hudson Eiver group, at Waynes- 

 ville, Ohio. The species occurs at other localities, and is often found in collec- 

 tions labeled as coming from Cincinnati, Ohio. 



Genus TELLINOMYA, Hall. 

 Tellinomya pectunculoides. 



Plate 1, fig. 24. 



Tellinomya pecimnculoides, Hall ; Descr. New Species of Fossils from the Hudson River 



Group, etc., p. 4 ; 1871. 

 Tellinomya pectuncukndes, Hall ; 24th Eept. State Cab., p. 228, pi. 7, fig. 26. 



The following is the description of this species, as given by Prof. Hall, 

 as above cited: 



" Shell small, sub-circular in outline, with the posterior end slightly 

 prolonged below the middle, giving a little obliquity to the shell ; pos- 

 terior cardinal border sloping to the point of greatest extension ; anterior 

 and basal borders regularly rounded ; beaks small ; general surface of the 

 valves depressed convex. Hinge plate strongly arcuate, more abruptly 

 curving in the middle, occupied by ten or twelve teeth on each side of 

 the center, those in the middle being nearly straight, becoming more and 

 more bent and angular toward the extremities ; muscular impressions- 

 large and distinct ; pallial line strongly marked, situated considerably 

 within the border of the valve. Surface characters of the valves not 

 observed." 



Among the specimens examined from Cincinnati there is a slab of 

 several inches square, covered with exfoliated specimens of this species, 

 some of which preserve the shell sufficiently to show that the surface was 



6 



