PRKSSTDENS 1077 



SiMPSONKi.LA CRASSA (Drouet). 



Shell long rhomboid, slightly narrower in front, subsolid, 

 convex or slight!}- inflated, inequilateral ; beaks not prominent, 

 their sculpture apparently zigzag-radial ; posterior ridge full, 

 imperfectly double, ending in a wide, feeble biangulation be- 

 low the median line ; dorsal line lightly curved ; base line 

 straight or nearly so ; anterior end rounded ; dorsal slope 

 obliquely truncated : sm-face with irregular, concentric sculp- 

 ture; epidemiis warm brown, subshining; teeth feeble or rudi- 

 mentary, lamellar, vestiges of both pseudocardinals and lat- 

 erals being present ; muscle scars shallow ; nacre pale purplish, 

 coppery-tinted, slightly thickened in front. 



Length 68, height 37, diam. 21 mm. 



Borneo. 

 Pseiidodon crassus Drouet. Jl. de Conch., XL. 1892, p. 93. — 



Drouet and Chafer, Mem. Soc. Zool. de Fr., V, 1892, p. 



15T, pi. VI, figs. 1-3. 

 Dolliella crassa Simi'Son, Syn., 1900, p. 834. 



Two fine specimens of this species from Banguey Islands, 

 North Borneo, received under the name Fscudodon insnlaris, 

 are in the National Museum collection. It is a smoother, more 

 inflated, rather more elongate form than iusiilaris, though 

 the two are closely related and, I believe, belong here instead 

 of with Pseiidodon. In the latter group the vestigial pseudo- 

 cardinals are stumpy and there are no laterals ; in Simpsonella 

 there are vestigial pseudocardinals and laterals, the whole be- 

 ing lamellar. 



Genus PRESSIDENS Haas, 1910. 



Prcssidens Haas, Nachr. Deutsch. Mai. Ges., 1910, p. 102. 



"Shell oval, thin. Beaks low, beak-cavities shallow ; beak 

 sculpture consisting of concentric ridges, each ridg'e made 

 up of two curves, which meet in a sharp ang"le on the oldest 

 part of the beak and gently curve with each other on the 

 younger part ; the anterior of these curves surrounds the front 

 of the beak in a semi-circle, the posterior curve is angularly 



