202 PLEUROBRANCHUS. 



Anus behind posterior insertion of gill. Genitalia in front of ante- 

 rior insertion, male and female organs contiguous. Total length of 

 body 26, width 18 or more, alt. 11 mill. 



Shell small, situated entirely in front of the middle of body, 

 nearly flat, calcareous and moderately strong, purplish-white. 

 Earlier portion convex, terminating in a minute spiral, later portion 

 becoming flattened, with flaring margins. Surface closely wrinkle- 

 striate. Interior concave above, with deep, coarse, concentric 

 wrinkles. Alt. 5*2, width 4 mill. 



Jaws large, component plates of the tessellation without trace of 

 lateral denticulation. Teeth of the radula simply hooked, with no 

 denticles. 



(Polynesian species). 



P. DELICATUS Pease. PI. 45, figs. 7, 8, 9. 



Shell small, rather solid, subpyriform, elongate, narrow posteriorly, 

 rounded in front, slightly flexuous ; surface rough and marked 

 with prominent lines of growth ; nucleus spiral ; anterior portion 

 stained with violet, posteriorly white or light horn color. 



Animal delicate, subpellucid, mantle smooth, oblong-oval, rounded 

 at both extremities, convex along the dorsal region. Foot elongate- 

 oval, rounded at both ends, entirely concealed by the mantle. Ten- 

 tacles slightly tapering to truncate tips. Oral veil somewhat con- 

 cave in front, produced laterally in tentacular form. Branchial 

 plume small, short. 



Color uniform orange-yellow throughout, the viscera imparting a 

 dark shade to the dorsal region. (Pse.). 



Huahine, under stones at low water mark (Pse.). 



P. delicatus PSE., P. Z. S., 1861, p. 245 ; Amer. Journ. Conch., 

 iv, p. 79, pi. 9, f. 1. 



The shell of this species (and of a few others to be hereafter de- 

 scribed) differs considerably from the usual form in being very nar- 

 row posteriorly, approaching that of genus Syphonota. (Pse.). 



P. OVALIS Pease. PL 46, figs. 16, 11, 17. 



Animal oblong- oval, smooth, subpellucid, convexly rounded 

 above, thin at the margins, rounded behind, slightly concave in 

 front. Foot oblong, nearly as wide as the mantle, and projecting 

 far posterior to the body. Tentacles well developed, smooth, 

 scarcely tapering, cylindrical, truncate and involute. Eyes black 



