244 Bulletin 39 416 



Genus CHIOME, Megerlevon Miihlfeld 

 Chione Rowleei, n. sp. Plate 30, figure 2 



Shell rather large, convex, ovate; lunule broadly cordate 

 and concentrically sculptured; escutcheon long, narrow, smooth 

 and defined by a small cord-like ridge; surface of the disk with 

 about 30 slightly elevated concentric ribs which on the umbos 

 are thin and lamellar but lower on the shell disk are wide and 

 trianglar at the base, but with a thin zigzag or fluted lamellar 

 ridge on top; the interspaces, much wider on the umbos is sculp- 

 tured with even rib-like cords which also flute in harmony the 

 dorsal face of the concentric ribs; the ventral face of the ribs are 

 finel}^ striated by radial incised lines which form cord-like ridges 

 along Yi as wide as the radial cord of the interspaces; interior of 

 the shell deep, with a small pallial sinus and subequal adductor 

 scars; basal margin finely crenulated as well as the lunular mar- 

 gin and the extreme posterior extremity. 



Length 42, height 37.5, thickness (right valve) 17 mm. 



This large, elegant Chione is quite common in the Gatun 

 beds of Costa Rica. It also occurs in the lower Gatun at Gatun, 

 usually in the form of casts. It recalls in a general way, the re- 

 cent West Coast C. amatJutsia Philippi, but differs in its heavier 

 shell, higher and fuller umbos and difference in details of its 

 .spiral and radial sculpture. In the Costa Rican shell, the radial 

 cords are simple, relating it more closely with the small C. 

 IVoodivardi Guppy of the Miocene of Jamica and Santo Domin- 

 go, while in C. amailuisia, xhty are double and alternating. 



The C. tegulum Brown and Pilsbry we have not seen. It 

 is a smaller shell, related to the C. Woodwardi. In C. tegulum 

 the concentric lamellae are much closer and the wide cordate 

 lunule is sculptured only with radial lamellae. 



It is named for Professor W. W. Rowlee, who collected a 

 few specimens from the Banana River in the course of botanical 

 investigation of the Balsa tree (Genus Ochroma), a very light 

 wood used in the construction of life-buoys, etc. 



