294 PROCEEDINGS OF THE ACADEMY OF [1897. 



course of a rather extensive search, I conclude it to be unpub- 

 lished. 



M. ventricosa Gray, from New Zealand, has similar weak lateral 

 teeth, but it is lower, shorter, and more swollen in the middle. 



Types are no. 70,486 coll. A. N. S. P. 



Corbula Lyoni n. sp. PI. VII, figs. 21, 22, 23. 



Shell solid and strong, nearly equivalve, very inequilateral, com- 

 pressed, oblong, the beaks near the anterior third; dorsal margin 

 straight and sloping posteriorly, convexly sloping in front; anterior 

 end wide, rounded ; posterior end narrow, obliquely truncate, ter- 

 minating below in an acute angle ; basal margin straightish in the 

 middle, rather abruptly rising near the posterior angle. Outer sur- 

 face dull whitish. Right valve slightly larger, noticeably surpass- 

 ing the left behind the beaks and along the posterior two-thirds of 

 the basal margin, where it closely overlaps the margin of the left 

 valve. The valves are about equal in convexity, and have the 

 same sculpture. A posterior area is conspicuously defined on each 

 valve by an acute keel running from the beaks to the posterior 

 angle; the keel is considerably bowed downward; above this the 

 surface is closely, sharply and subregularly costulate, the riblets 

 straight, obliquely descending in the direction of growth lines. In 

 front of the keel, the basal half of the valves, or more, has very 

 coarse and irregular concentric folds ; on the rounded anterior end 

 the folds become more regular and more numerous. The upper part 

 of each valve is free from the coarse wrinkles or folds mentioned, 

 being merely striated rather irregularly in the lines of growth. 

 Interior flesh colored, sometimes in part olive-yellow, the margins 

 of the valves of the latter color. In the right valve there is a re- 

 curved, triangular, acute tooth. 



Length 11 "75, height 6*75, diam. 3*9 mm. 



Length 12'75, height 7*9 mill. 



Maldonado Bay, Uruguay, in 3 to 6 fms. 



This species is remarkably similar in form and sculpture to Cor- 

 bula Macgillivrayi E. A. Smith, 8 described from south of New 

 Guinea, in 28 fathoms. Mr. Smith's species, however, is double the 

 size of C. Lyoni ; it has minute sculpture not seen in the latter ; 

 the ribbing of the posterior area is coarser, and the wrinkling of 



8 Keporton the ''Challenger" Lamellibranchiata, Chall. Rep. Zoology, 

 Vol. XIII, p. 30, pi. x, figs. 8-86 (1885). 



