200 PLEUROBRANCHUS. 
Lingual teeth simple, not denticulate, the shape of a horse’s jaw, 
rather acute at apices, lightly bent. Shell small, elongated, nearly 
flat, with a linear, radial, submedian impression; lire of growth 
strong and remote, the interstices a little concave, lirule of growth 
solitary, small. Color chestnut, whitish toward the periphery ; 
length 6 mill. (Morch). 
St. Thomas, West Indies (Riise). 
Pleurobranchus areolatus Morcu, Journ. de Conchyl., 1863, p. 
28; Malak. BI., xxu, p. 178. 
This may, perhaps, be an Oscanius. 
P. crrcuLARIS Morch. 
Mantle circular, gelatinous, white or pale isabelline, subpellucid ; 
periphery thick, semiterete, margin prone, inflexed, acute, the edge 
submembranous-circular ; foot elongate-oval, margin undulating, - 
with very short, transverse remote sulci; anteriorly broadly 
rounded, sinuous in the middle, destitute of the transverse sulci of 
the fore part, rather acute behind, with an oblique, funnel-shaped 
sulcus, slightly glandular. Veil lunar-reniform, slit at sides. Ten- 
tacles approximate at bases, diverging, acute, incurved, conic, slit 
along the sides; eyes situated below their external bases, incon- 
spicuous, deeply sunken. Gill plume adherent for its entire length, 
the rachis smooth with 16 alternating plumules on each side. 
Anus in front of end of plume. Shell small, median, white, seen 
through the transparent mantle. 
Diam. mantle 31 mill.; length of foot 25, width 123; width of 
veil 10, length in middle 3 mill. 
St. Thomas, West Indies (Riise). 
Berthella circularis Morcu, Journ. de Conch., 1863, p. 31. 
This species and the preceding are known only by Moérch’s de- 
scriptions. 
P. paraconicus d’Orbigny. PI. 74, figs. 92, 93. 
Body quadrilateral, depressed, amber colored, of a deeper tint in 
the middle of the mantle, paler on gills and soles. Mantle oblong, 
rounded at the ends, narrower than the foot, entirely smooth, the 
edges thin and sharp, not covering the gill. Foot squarish, very 
wide, extending beyond mantle all around, its edges thin. Head 
moderate, rounded, without buccal appendages. Tentacles 2, flat 
and somewhat channelled. Gill conic. Genital orifice forming a 
