FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 203 



Conocardium cuneus. CONRAD. 



Plate V., figures 10 to 19. 



Pleurorhynchus cuneus, Conrad. Geol. Surv. N. Y. Ann. Hep. 1840. 

 Pleurorhynchus trigonalis, Hall. Geol. Surv. N. Y. Rep. 4th Dist., p. 171 1843. 

 Conocardium trigonale, Hall. Pal. N. Y., Vol. 5, pt. 1, pis. and exp. 1883. 

 Conocardium cuneus, Hall. Pal. N, Y., Vol. 5, pt. 1, page 409 1884. 



Shell large ; shape very difficult to compare with any generally known form ; 

 its side-view is more or less sub-trigonal, and its dorsal or ventral view angu- 

 larly sub-ovate. The proportion of its length to its height varies considerably ; 

 the length is always greater than the height, but never becomes twice as large 

 as the latter. 



The basal margin is gently curved from the posterior extremity to the an- 

 terior end. The posterior extremity is abruptly truncated, and produced into 

 a tubular extension alone: the cardinal line. This tubular extension attains, 

 in some shells, a considerable length, and is supposed to serve as a siphuncle. 

 The truncated rear end is very large in extent, and cardiform in shape ; it is 

 usually concave, with the exception of the part near and around the siphuncle, 

 which is more or less convex. 



Cardinal line straight ; its margins, anterior to the beaks, are inflected. An- 

 terior end more or less rapidly contracting, with the margins gaping before 

 reaching the extremity. Valves entirely equal, and more or less gibbous. The 

 beaks are prominent and closely incurved over the hinge-line; they are situated 

 near the center. 



The umbonal ridge is acutely angular, forming the line of demarcation be- 

 tween the lateral and posterior surfaces ; it extends from the beaks to the pos- 

 terior extremity in basal margin. Test thick, composed of two distinct 

 layers. 



Surface marked by numerous radiating plications, and intermediate arching 

 lamellose, concentric striae on the body of the shell. The posterior surface 

 is ornamented by regularly curving radii, circling around the base of the 

 siphuncle. From the entire periphery of the umbonal ridge extends an ex- 

 pansion of the shell, called the shield, increasing in extent from the beaks 

 downward to the posterior extremity of the basal margin. This shield is 

 covered with fine striae, running parallel with the basal margin. In some 

 specimens, we notice at the extreme rear end of the body of the shell, where 

 the shield has been removed, a long, slender, cylindrical tube in the extension 

 of the basal line. What purpose it serves is not known. The valves are 

 finely crenulated at the margins. Prof. Hall has united different forms, which 

 were heretofore considered different species, into Con. cuneus ; he retains the 

 abandoned species, however, as varieties, which are as follows : 



