682 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxiii. 



into a number of stages formed by the variation in the strength 

 of the incised lines. In the type there are five, tlie first being im- 

 mediately below the nepionic portion, while the rest divide the re- 

 maining part into equal segments. The narrow darker l^ands, repre- 

 sented by irregular stronger sculpture, may mark resting periods. In 

 addition to the incised concentric sculpture the entire surface is 

 marked by microscopic crinkling, especially in the grooves. Interior 

 bluish-white. Hinge slight, long, curved. Ligament rather short, 

 partly internal Cardinals: in the right vaive one, decidedly curved 

 and nnich stronger and more elevated posteriorly where it bends 

 downward over the hinge plate; in the left valve two, the upper slen- 



CORNEOCYCLAS DAVISI BaRTSCH. MAGNIFIED f. 



der and obliquely curved and but slightly elevated, the lower small, 

 somewhat triangular and a little more elevated than the upper. Lat- 

 erals: double in the right valve, slender, curved, lamelliform, the 

 ventral considerably more strongly developed than the dorsal ; single 

 in the left valve, the anterior one bearing a cusp-like projection on 

 its middle, while the posterior one is best developed at its posterior 

 extremity. 



The shells of fresh specimens, when viewed by transmitted light, 

 appear uniforml}^ very minutely dotted as if finely punctured. 



The type measures: Length 5.0 mm.; height 4.0 mm.; diameter 

 2.7 mm. The largest specimen, a single valve, measures: length 0.0 

 mm. ; height 4.9 mm. 



The lot, consisting of the type and two complete specimens and two 

 single valves, is entered as Cat. No. 198053, U.S.N.M. 



