298 PROCEEDINGS OF THE ACADEMY OF [Nov., 



ovate, outer and basal margins obtuse. The columella is weakly 

 concave and somewhat thickened. The parietal callus is moder- 

 ately thick. There is no operculum. 



Length 10.6, diameter 6.75, apeiture 4.8 mm. 



Length 9.2 mm. Smallest adult. 



Hilo, Hawaii, on the sea urchin, Diadema. D. Thaanum. 



The apical point is more or less worn away in the adult stage. A 

 young one, 3 mm. long, is figured showing it perfect. Mr. Thaa- 

 num writes that he did not find this Stylijer on any other species of 

 sea urchin, though many others were examined. 



Fig. 2. — a, b, Slylifer mittrei Petit, adult and young; c, Siylifer thaanumi n. sp. 



This form agrees so exactly with that described without definite 

 locaUty by Petit (Journ. de Conchyl. II, p. 27, pi. 2, figs. 8, 9) that 

 the identity can scarcely be doubted. I am inchned to think that 

 it was a distinct species which Schepman and Nierstrasz^ had under 

 the name Mucronalia mittrei from Sumbawa. It was operculate, 

 6 mm. long, 4 wide. 



Mucronalia tumida Pse., mentioned by Tryon as identical with 

 8. mittr-ei, is certainly distinct from that species. 



Stylifer thaanumi n. sp. Fig. 2 c. 



The shell is shortly ovate with slender summit, white, glossy and 

 smooth, growth-striae being scarcely noticeable. About 5 early 

 whorls form the slender summit, but the transition to the broad 

 later portion of about 3 whorls is gradual. The last whorl is glo- 

 bose. Suture impressed, not margined. Aperture ovate. Outer 

 and basal lips evenly curved, blunt; columella shghtly concave, a 

 little thickened. Parietal callus distinct but rather thin. There is 

 no operculum. 



^ Siboga-Expeditie, Parasitisolie Prnsnbranohior dor Siboga-Expoclition, p. .3. 



