- 107 - 



AROA (OALLOAROA) IimSITATA n. sp. 



Description .- Shell of nerli-um size, higli, soraev/hat compress- 

 ed, irregular; posteriorly a'cliquely truncated above and produc- 

 ed below,'; irregularly rounded anteriorly; anterior portion of the 

 ventral margin distorted by the long, -."ide by._;sal gape; urabones 

 relatively low, broad, decidedly prosogyrate, at about the anter- 

 ior third of the length; posterior ridp-e prominent, the region be- 

 hind the ridge being excavated; external surface sculptured ?ath 

 numerous, very narrow, irregular radial ribs, occasionally dicho- 

 tomous and the interspaces occasionally bearing intercalated nar- 

 rower secondary ribs; interspaces usually narrower than the ribs; 

 the posterior slope sculptured witi: four ribs much coarser than the 

 others; concentric sculpture of irregular growth lines and occas- 

 ional raised lines, the two producing in certain oortions of the 

 shell a feeble semi-reticulated sculpture; cardinal area relative- 

 ly short and wide, conspicuously marked by six or seven concentric 

 ligament grooves; hinge gently arched; anterior teeth irregi^lar, 

 median teeth very short, almost obsolete, posterior teeth large, 

 oblique; inner margin of the shell smooth or ";ith faint crenu- 

 lations. 



Dimensions .- len-th, 31.5 mm.; alt. 22 mm.; semidiam. , 7.8 

 imn. ; length of hinge 12 mm. 



