204 PLEUROBRANCHUS. 
more obtusely rounded before than behind. Surface above convex, 
and coarsely marked with concentric wrinkles; nucleus posterior 
and lateral, forming a small cavity at that portion of the shell. 
Length 5 lines (Pse.). 
Sandwich Is. (Pse.) 
Pleurobranchus pellucidus Psx., P. Z.8., 1860, p. 24. 
P. MARGINATUS Pease. 
Form oval, smooth, convex above and subpellucid. Mantle 
widest at the middle, rounded behind and truncately rounded in 
front, and concealing the foot. Tentacles rather long, stout, grooved, 
truncated, and cylindrical. Oral veil triangular. Foot oblong 
oval. Color pale lemon yellow, freckled with white and mar- 
gined with light red. Shell ovate, thin, fragile, pellucid, whitish 
horn-color, with a dull red tinge near the nucleus. Nucleus sub- 
spiral. Strize of growth coarse. (Pse.). 
Sandwich Is. Under stones in the lower region of the littoral 
zone (Pse.). 
P. marginatus Psx., P. Z.S., 1860, p. 25, No. 18. 
P. RuFus Pease. 
Form oval, smooth and convex above. Mantle concealing the 
foot, widest at the middle, rounded behind, and somewhat concave in 
front. Tentacles stout, truncated, grooved and cylindrically taper- 
ing. Oral veil subtriangular. Branchiz tripinnate, with the 
pinnae arranged alternately. Foot oblong oval, rounded at both 
ends. Color uniform vermilion. Length 1 inch. (Pse.). 
Sandwich Is. Under stones in the lower region of littoral zone. 
P. rufus Psx., P. Z.8., 1860, p. 25, No. 19. 
P. VARIANS Pease. 
Oval, rather rugose, convex above. Mantle rounded behind, 
deeply sinuose in front, and margins slightly undulated. Tentacles 
arising from the head, curving laterally, deeply grooved below, 
truncated, cylindrically tapering, transversely lamellated. Eyes at 
their posterior bases. Oral veil large, convex in front, and much 
dilating laterally, where it is deeply grooved. Mouth proboscidi- 
form. Branchial plume simple, pinnate on the middle of the right 
side. Foot large, reaching the edge of the mantle laterally and 
behind. Color varying; some bright red, others lemon-yellow, or 
purplish brown, others again variegated with whitish; beneath 
