MUSEUM OF COMPARATIVE ZOOLOGY. 315 



The species extends northward to Cape Hatteras, and the smaller valve is fre- 

 quently of a pink color or pinkish brown. It reaches a length of 8.0 mm., 

 and is very variable in its proportions and sculpture. I have no doubt that it 

 is the operculata of Philippi, but the C. Krebsiana of C. B. Adams is a different 

 Rnd more delicate species. 



Corbiila (Taeniodon?) cymella Dall. 



Corbula cymella Dall, Bull. M. C. Z., IX. p. 115, 1881. 



Plate I. Fisrs. 7, 7 a. 



Habitat. Gordon Key, 68 fnis., one living specimen, 13.5 mm. in length. 



The accidental fracture by the draughtsman of one valve of the unique, speci- 

 men enabled me to get at the hinge. I found it very delicate, the right valve 

 with a single small slender tooth, behind which is a very small cartilage set in 

 a short groove in the hinge-margin, and continuous above with a darker-colored 

 linear substance, which may have been a bit of thicker epidermis than ordinary, 

 but looked like a linear external ligament covered only by the coil of the umbo. 

 The left valve had a smooth edentulous hinge margin, with the cartilage en- 

 tirely on top of the small thin horizontal process behind the beak. 



Another feature omitted in the original diagnosis is, that the very fine radi- 

 ating lines, which cover the shell and are most noticeable on the posterior 

 supra-carinal area, are minutely granular. The thin and hardly unequal valves, 

 and the marginal, if not exposed, cartilage of this species, suggest a modification 

 in the direction of Tceniodon. 



The following three species were not represented in the collection, 

 but, in view of their not having been figured and thus being placed in 

 doubt in the catalogues, it was thought worth while to include the 

 camera-lucida sketches of the types and a synopsis of the remarks of 

 Professor Adams in regard to each of them. 



Corbula Krebsiana C. B. Adams. 



a Krebsiana Ad. Contr. to Conch., p. 234, Oct. 1852. 



Plate I. Fiffs. 1, la, lb. 



Shell trigonal, very inequivalve, inequilateral, with the large valve ros- 

 trated; the ventral margin rounded anteriorly, nearly straight posteriorly; 

 white, often tinged with pink, except posteriorly; small valve finely concen- 

 trically striated; large valve finely and closely furrowed; beaks prominent, 

 much involuted, umbones very convex; with small posterior angles, one on 

 the small valve and two on the other: teeth small. Lon. 6.1; alt. 5.1; diam. 

 3.8 mm. 



