264 Bulletin 39 436 



ed internals molds. It is related to the recent Pacific H. elegans 

 Sowerby, but differs in being less convex, wider and with more 

 numerous and closer concentric plicae. 



Gatu7i Stage; Coll. 6. Estrella River. 

 Coll. 2, Quitana creek. 



Mactra sincola, n. sp. Plate 28, figure 4 



Shell thin, broadly subtrigonal, depressed, nearly equilater- 

 al; beaks small and pointed anteriorly; lunule absent; escutche- 

 on linear-lanceolate and defined from the shell disk by an elevat- 

 ed carina; the surface is sculptured with strong, wave-like, con- 

 centric plicae which are continuous from the anterior-dorsal mar- 

 gin to the edge of the escutcheon; on the t}^pe specimen there 

 are about 30 plicse on the center of the shell disk, spac ed about 

 1.75 mm apart; the intervals between the concentric plicae 

 are deep and trough-like and in width equal to the plicae them- 

 selves; in addition the whole surface of the shell is finely sculp- 

 tured with small, radial, vermiculate threads, best seen on the 

 summits of the plicae; the escutcheon is ridged on the middle 

 and smooth; the hinge, largely concealed in the sandy matrix, is 

 mactroid. 



Length 36, height 27, diameter of the right valve 5.5 

 mm. 



The systematic position of this interesting shell is very 

 doubtful. Its general surface sculpture of strong, concentric 

 plicae and well-defined escutcheon resembles that of Harvella. 

 The surface is covered with fine, vermiculate threads as seen on 

 Labibsa. 



Gatun Stage: Satiry creek. 



Genus LABIOSA, (Schmidt) Moller 



Labiosa lineata Say Plate 21, figure 11 



Lutraria lineata Say, 1821, Journ. Acad. Nat. Sci. Phila., vol. 2, p. 

 310. 



