242 



BUI^LETTN 39 



414 



continuation of the concentric ribs and lamellae; escutcheon lan- 

 ceolate, bordered by an angled ridge from the shell disk; disk 

 sculptured with about 28 even, concentric ribs which appear 

 as close undulations of the shell surface; the ribs and inter- 

 spaces are in addition sculptured with fine laniell^-like threads, 

 each finely crenulated or radiall\^ striated; these lamellae vary in 

 size, those of the interspaces or troughs between the ribs are fine 

 and 5 in number, with 2 large ones forming the tops of the ribvS 

 themselves, so that the ribs appear as if mesially divided; the 

 radially striated character of the ribs and lamellae is much strong- 

 er on the anterior and posterior submargins; interior of the shell 

 deep but concealed by matrix in the type specimens. 



Length 21.5, height 19.5, diameter 6.25 mm (right 

 valve). 



This elegant species occurs in the coralline phase of the 

 Gatun formation in Costa Rica. Its relations are with the A. 

 Blajidiana Guppy and the recent A. strigilli7ia Dall, but differs 

 from both in its more elegant sculpture. This sculpture consists 

 of close, regular, wave-like undulations or ribs, the crests of 

 which carr}^ 2, low laminae, the troughs or interspaces, 5 or 6 

 finer threads. These fine thread-like laminae are delicately etch- 

 ed with fine radial striations. 



It is named for Professor G. D. Harris of the Paleontologi- 

 cal Department of Cornell University. 



Gatun Stage: Port Limon. 



Genus CYCLSNELLA, Dall 



Cyclinella beteyensis, n. sp. Plate 31, figure 2 



Shell thin, Dosinoid or sub-circular in form, the margins of 

 the shell nearly a perfect circle; slightly convex; beaks small 

 but distinct, situated at the anterior ^ of the shell ; sculpture 

 with very fine, concentric threads, which are a little elevated and 

 strongest on the anterior end, nearly smooth on the middle; lu- 

 nule small, lanceolate and defined by a small, incised line; hinge 



