490 DR WHEELTON HIND ON 



Ambonychia undata, Emmons, sp., 1842. (PI. I., fig. 30.) 



Pterinea undata, Emmons, 1842, Geol. Rept. New York, p. 395, fig. 1. 



Inoceramus vetusfus, Sow., var. priseus, Portlock, 1848, Rept. Geol. Londonderry, p. 423, pi. xxxiii. 



figs. 1, 2, 3. 

 Ambonychia undata, Hall, 1847, Pal. New York, vol. i. p. 165, pi. xxxvi. figs, la, b. 



Specific Characters. — Shell oblique, triangularly ovate, obliquely gibbose in front, 

 compressed, and subalate posteriorly. Anterior end obsolete, adpressed to form a 

 broad anterior surface. The anterior margin slopes downwards and backwards ; the 

 inferior margin rounded, posterior truncate, straight, oblique, making an obtuse angle 

 with the hinge line, which is straight and as long as the transverse diameter of the shell. 

 The umbones are terminal, bluntly pointed, very little elevated above the hinge line. 



Interior. — Unknown. 



Exterior. — The surface has an ornament of several broad concentric bands, 

 separated by shallow sulci of about the same breadth as the bands. 



Dimensions. — Fig. 30, PL I., a left valve, measures : antero-posteriorly, 10 mm. ; 

 dorso-ventrally, 9 mm. 



Locality. — Scotland : Llandeilo beds, Ardmillan. 



Observations. — Portlock, though he referred his species to the Carboniferous shell 

 described by Sowerby as Inoceramus vetustus, recognised that his species did not agree 

 exactly with that shell, and gave it the varietal name of priseus. It is interesting 

 to note the homomorphy of the Llandeilo A. undata, the Carboniferous Posidoniella 

 vetusta, and Cretaceous Inocerami. All these genera, absolutely distinct in their 

 hinge characters, have a similar external ornament. A. undata is rare in the Gray 

 Collection, and the specimen is much smaller than that figured by Portlock or Hall. 



Ambonychia quadratus, sp. nov. (PL II., figs. 1-3.) 



Specific Characters. — Shell subquadrate, gibbose, oblique. The anterior end 

 obsolete ; the border, raised, thickened, rounded and incurved, descends with a gentle 

 convexity and gradually becomes flattened to join the broadly convex lower margin. The 

 posterior border is somewhat truncate, rounded below where it joins the inferior margin, 

 and making a well-marked, somewhat obtuse angle with the hinge line above. The- latter 

 is straight and produced. The umbones are large, incurved, and somewhat prosogyrous, 

 not contiguous, anterior. The dorsal slope is much compressed, the posterior superior 

 angle subalate. The greatest convexity of the valve is anterior and subumbonal. 



Anterior. — The hinge plate seems to be plain except at the posterior end, where 

 there are three small oblique lateral teeth separated by fine grooves. 



Exterior. — The surface is ornamented with fine concentric striae and lines of growth. 



Dimensions. — Fig. 2, PL II., measures: antero-posteriorly, 55 mm.; dorso- 

 ventrally, 46 mm. ; elevation of valve, 10 mm. 



Localities. — Penkhill, Upper Llandovery ; Woodland Point, Middle Llandovery ; 

 Mulloch Hill, Lower Llandovery ; Balclatchie, Ardmillan, Llandeilo series. 



