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, submediaii impression ; lirse of growth 

 strong and remote, the interstices a little concave, lirulse of growth 

 solitary, small. Color chestnut, whitish toward the periphery; 

 length 6 mill. (3/orc/i). 



St. Thomas, West Indies (Riise). 



Pleurobranchus areolatus MORCH, Journ. de Conchyl., 1863, p. 

 28; Malak. BL, xxii, p. 178. 



This may, perhaps, be an Oscanius. 

 P. CIRCULARIS 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 12* ; width of 

 veil 10, length in middle 3 mill. 



St. Thomas, West Indies (Riise). 



Bertfiella circiilaris MORCH, Journ. de Conch., 1863, p. 31. 



This species and the preceding are known only by Morch's de- 

 scriptions. 



P. PATAGONICUS 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 



