TRENTON LIMESTONE. 165 



214. 3. AMBONYCHIA AMYGDALINA (n. *;).). 



Pl. XXXVI. Figs. 6 a, b, e. 



Obliquely ovate or elliptical, with the umbones extended, height much greater than the 

 length ; umbones oblique, nearly parallel to the anterior margin, and bending forward at 

 the apices ; anterior margin obtuse, straight for a short distance below the beak, and thence 

 broadly curving around to the base ; surface regularly convex in the middle, becoming 

 gibbous above ; posterior margin compressed, subalate. 



The only specimen known is a c£ist, from which the figures and descriptions are taken. 

 It will be readily recognized by the form, which differs from that of any other species. 

 The lower part of the specimen presents a very regular elliptical figure, intercepted above 

 by the oblique direction of the umbones, which are slightly curved forward at the extremi- 

 ties. The anterior edge presents a distinct oblong lunule beneath the apices of the umbones. 

 A few obscure undulations are visible upon the cast, but nothing from which the character 

 of the original surface can be ascertained. 



Fig. 6 a. Right valve of this specimen. 

 Fig. 6 A. Profile from the posterior side. 

 Fig. 6 e. Profile of the anterior extremity, showing a kind of lunule below the beaks. 



This species resembles in form Inoceramus rostratus, a species from the Lias (Goldfuss, 

 Petrefada, Vol. ii. pag. 110, tab. 115, fig. 3 a, i). 



Position and locality. In the higher part of the Trenton limestone at Adams, Jefferson 

 county. Its associates are Murchisonia, Pleurotomaria, Atrypa bisulcata, and fragments of 

 Orthoceratites. 



215. 4. AMBONYCHIA UNDATA. 



Pl. XXXVI. Figs. 7 a, b. 



Pterinea undosa. Conhad in MS. 



— undata. Emmons, Geol. Report, 1842, pag. 393, fig. 1. 



Compare Inoeeramut vettutus, Sowerby, Min. Conchology, 1829, Vol. vi. pag. 102, tab. 584, fig. 2. 



— — VM.prucus, PoRTLOCK, Geol. Report, 1843, pag. 423, pl. 32, figs. 1, 2, 3. 



— — Goldfuss, Petrefacta, 1834 - 1840, Vol. ii. pag. 107, tab. 108, fig. 5. 



Obliquely ovate or subrhomboidal, with the base rounded, ventricose ; anterior margin 

 obtuse, straight above and curving below ; posterior margin compressed, scarcely alate 

 above ; cardinal line straight, oblique ; umbones ventricose, elevated, narrowing above 

 and scarcely incurved, with the extremities bending forward ; surface with broad, smooth, 

 concentric undulations, which curve downward more abruptly on the centre of the shell ; 

 anterior side scarcely concave below the beaks ; no definite lunette. 



