940 PALEONTOLOGY OF NEW-YORK. 



Itli} uclioiiella iiobilis ( u. s.)- 



Plate XLIII. Fiq. 3a-/. 



Shell varying from compressed ovate to subrhomboidal, becoming in adult 

 specimens broad ovate and much more gibbous. Dorsal valve the larger, 

 elevated in front into a somewhat rounded mesial prominence which 

 rarely extends beyond the middle of the shell, declining laterally with 

 an abrupt curve to meet the inflected edges of the opposite valve : beak 

 incurved. Ventral valve depressed ( in old specimens), abruptly inflected 

 at the margins towards the opposite valve, depressed towards the front 

 into a shallow rounded mesial sinus, sometimes prolonged into a vertical 

 extension with nearly parallel sides : beak small, not prominent, in- 

 curved. 



Surface marked ,by twenty-six to thirty-two strong angular plications, 

 six to eight of which are elevated on the mesial fold of the dorsal valve, 

 and five to seven depressed in the sinus of the other valve. Fine closely 

 arranged zigzag lines of growth may be seen near the margins of the 

 valves in front. 



This species holds a position between R. abrupta and R. campbellmta : it is, how- 

 ever, always more elongated than the first, and not so much so as the latter. It also 

 resembles Terebratula eucharis of Barrande ( Silur. Brach. aus Bcehmen, PI. xvii, 

 f. 2); but is more gibbous in old specimens, and more elevated in front, as well as 

 more finely plicated. 



Fig. S a, b. A young specimen with a scarcely defined sinus. 



Fig. 3 c, d, e,f. Dorsal, ventral, front, and profile views of an individual of medium size. 



Fig. Z g, Ji. Dorsal and front views of a larger and more gibbous specimen. 



Fig. 3 I, k. Dorsal and front views of the largest and most vontricose form that has been 



observed. 

 Fig. 3 / [ by error marked 3 6 ]. A cast of the ventral valve of this species. 



Geological positum and locality. In the Upper Pentamerus limestone, Albany and 

 Schoharie counties. 



