No. 109.] 185 



Solt7i and Solccurtus ; especially, as I believe to be the case, that the se- 

 ries of cardinal teeth is uninterrupted by a fosset, which in Nucula is a 

 prominent character. This genus, so constituted, is restricted to the Silu- 

 rian, and perhaps to the Carboniferous system." 



CUCULLELLA. 



M'CoY, Ann. Nat. Ilistorv, 2d series, vol. vii, p. 50; British Pal. Fossils, p. 283, 



1855. 



" Generic Characters. Subrhomboidal, inequilateral, subequi- 



valve; margin even ; hinge-line entirely crenulated ; muscular 



impressions two, with a simple pallial scar between them ; a 



strong internal septum extends from before the beaks to the 



posterior margin of the adductor muscle, forming a deep slit 



in the casts ; surface generally smooth, or nearly so." 



"These palaeozoic shells have been confounded with Nuaila (Sow., 



Phil. &c.), from which they differ in the absence of the ligamentary pit 



in the hinge, and in the anterior internal septum : they have also been 



confounded with CucuUea, from which they differ in wanting the hood-like 



plate of the posterior adductor, and having the septum in the anterior end ; 



and with Clidophorus ( Greol. Surv. of Great Britain), from which they 



differ in having the hinge crenulated as in Arca.''^ 



The Genus Lyrodesma of Conrad was constituted to receive a 

 small shell which occurs in the shales of the Hudson-river group, 

 and which, but for certain restrictions in the generic description, 

 might include those here referred to Tellinomya. 



LYRODESMA ( Conrad ). 



Generic Characters. "Equivalved, inequilateral ; hinge-line with 

 eight diverging prominent cardinal teeth, transversely striated." 

 Mr. Conrad remarks that he "was fortunate enough to obtain two fine 

 casts of this bivalve, with the teeth remarkably well represented." The 

 figure given by Mr. Conrad, to illustrate this fossil, shows the hinge-line 

 with a continuous series of eight teeth. The typical species is L. plajia. 



I have refered to this genus a small shell from the Utica slate, which is 

 nearly equilaterial, with equally rounded extremities, and a few distinct 

 teeth on each side of the beak. This shell, L. pulchella, does not differ 



