234 Bulletin 39 406 



species is more depressed, less circular and more trigonal in out- 

 line. Gabb's species may prove to be but a small form of the 

 recent West Indien G. cerma C. B. Adams, 

 Gahin Stage; Port Linion. 



Old Man Sam creek, i mile soztth of the beach. 



Gafrarinm altum Dall, va. costaricensis, n. sp. Plate 32, figures 19, 22 



cf. Gafrariuin altuin Dall, 1903, Trans. Wagner Free Inst. Sci., vol. 3, 

 pt. 6, p. 1249, pi. 57, fig. 5, 

 Shell small, high, rounded trigonal, moderately convex; 

 beaks small and pointed slightly forward, in young shell nearly 

 central but becoming vvdth maturity slightly anterior; anterior 

 and posterior extremities nearly similiar and evenly rounded; 

 surface with fine, concentric lines, most distinct and even to- 

 wards the ventral margin, and with faint, radial striae on the 

 anterior and posterior slopes; lunule large, lanceolate, defined b}'' 

 an impressed line; interior of shell deep, with a concentrically 

 grooved margin. 



Length 4.85, height 4.75, diameter of right valve 1.50 

 mm. 

 The Costa Rican shells differ from the typical altum, de- 

 scribed by Dall from the Oak Grove sands of Florida, in being 

 more trigonal in form and with higher beaks. The sculpture of 

 its surface is mainly concentric, the radials showing only as 

 very faint striae on the posterior and anterior extremities. 

 Gatun Stage: Middle creek. 



Coll. 6, Est7'ella River. 



Genus MACROCALLISTA, Meek 



Section CHIONELLA, Cossmann 

 Macrocallista maculata Linn^us Plate 31, figures 6, 7 



Venus maculata Linnaeus, 1758, Syst. Nat., ed. 10, p. 686, ed. 12, p. 



1132. 

 Cytherea dariena Conrad, 1857, Pacific R. R. Report, vol. 6, p. 72, pi. 

 5, fig- 21. 



