302 paleontology of new-york* 



Genus LYRODESMA (Conrad). 



Character. " Equivalved, inequilateral; hinge with about eight diverging; prominent 

 cardinal teeth, transversely striated." 



If this description, cited from Mr. Conrad, were so altered as to include shells with a 

 greater number of cardinal teeth, it would include a species which appears Closely allied 

 to the one described as the typical form. The form of this shell, and character of the 

 diverging cardinal teeth, or crenulations, are different from Nucula, and more nearly like 

 Pectunculus. I prefer, however, to place it under the Genus Lyrodesma, provisionally ; 

 though a better knowledge of L. plana, the typical species of the genus, may hereafter 

 render it necessary to separate them. 



361. 1. LYRODESMA PLANA. 



Pl. LXXXII. Figs. 11 a, ft. 

 Lyrodesma plana. Conrad, Ann. Geol. Report, 1811, p. 51. 

 " Subrhomboidal, compressed ; posterior margin widely and obtusely truncated ; posterior 

 basal margin rectilinear; extremity rounded." 



I have copied the figures and description of Mr. Conrad, not having seen the shell. 

 It is described in the Annual Report cited above, and also figured on a plate partially 

 prepared for his report on palaeontology. 



Fig. 1 1 a. The right valve. 1 1 b. Interior of the right valve, showing the cardinal teeth. 

 Position and locality. In the shaly sandstones of the Hudson-river group near Rome, 

 Oneida county. 



362. 2. LYRODESMA PULCHELLA. 



Pl. LXXXII. Figs. 12 a, b, c, d. 



Slightly inequilateral, broadly oval ; beaks moderately elevated ; anterior extremity 

 rounded; posterior extremity scarcely truncated ; hinge line gently arched, marked by 

 about eight diverging teeth on the posterior side of the beak, and apparently fewer ( five 

 or six ) on the anterior side ; surface marked by fine equal concentric striee. 



This is the most beautiful shell among the bivalves of this group ; its nearly symmetrical 

 form, finely striated surface, and crenulated hinge line, are sufficient to distinguish it from 

 any other species. It is usually compressed, and but slightly convex ; hut wlien found in a 

 perfect condition it is very convex, and even ventricose towards the umbones. 

 Fig. 12 a. A specimen of the natural size, from the black slate near Watertown, Jefferson county. 

 Fig. 12 b. The same enlarged, showing the character of the crenulations. 



Fig. 12 c. A smaller specimen, from the partially altered slates near Waterford, on the Hudson river. 

 Fig. 12 d. The cardinal line enlarged. 



Position and locality. This species occurs in the loWer part of the group at Turin, and 

 near Watertown, in the unaltered slates; and near Waterford, in the black glazed slates 

 of the same group. 



