TRENTON LIMESTONE. 1G5 



214. 3. AMBONYCHIA AMYGDALINA (n. sp.). 

 Pl. XXXVI. Figs. 6 a, ft, c. 



Obliquely ovate or elliptical, with the iimboncs extended, height much greater tiian the 

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

 the apices ; anterior margin obtu.se, 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 cast, from which the figures and descriptions arc 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 lunbones, which are slightly curved forward at the e.vtremi- 

 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 b. Profile from the posterior side. 

 Fig. 6 c. Profile of the anterior extremity, showing a kind of limule below the beaks. 



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

 Petrcfada, Vol. ii. pag. 110, tab. 115, fig. 3 a, 6). 



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

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

 Ort/ioceratites. 



215. 4. AMBONYCHIA UNDATA. 



Pl. XXXVI. Figs. 7 a, ft. 



Plerinea undosa. Conrad in MS. 



— undata. Emmons, Geol. Report, 1842, pag. 39.'), fig. 1. 

 Compare Inoceramus vttuslus, Sowerby, Min. Conchology, 1829, Vol. vi. pag. 102, tab. 5S1, fig. 3. 



— — var. priscus, Portlock, Geol. Report, 1843, pag. 423, pl. 32, figs. 1, 2, 3. 



— — Goldfuss, Petrefacta, 1S34 - 1S40, Vol. ii. pag. 107, tab. lOS, 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 scnrcely concave below the lieaks ; no definite lunette. 



