210 HALIOTINELLA, GYMNOTOPLAX. 
H. MONTROUZIERI Souverbie. PI. 71, figs. 66, 67. 
Shell umbilicated, ovate-oblong, testacella-shaped, very thin, fra- 
gile, much depressed; apex flat, subsinistral ; white, pellucid, coy- 
ered by a thin straw-colored epidermis. Whorls 4, separated by a 
depressed suture, rapidly increasing, the earlier 3 rounded, last very 
ample, planulate, forming nearly the whole shell, concentrically 
subplicate-striate. Aperture elongate-oval, very large, shining 
within, the margins separated; right margin acute, left margin ar- 
cuate, incurved toward the right, channelled outside above, vault- 
ingly reflexed over the small umbilicus at the insertion, and con- 
nected with right margin by a callus. Length 14, width 7, alt. 23 
mill. Aperture 133 mill. long, 5 wide. (Sowv.). 
Island of Art, New Caledonia (Montrouzier). 
Haliotinella montrouzieri Souv., Journ. de Conchyl., 1875, p. 33, 
pl. 4, f. 1.— Cf. Morch, J. de C., 1876, p. 374. 
H. patinaria Guppy. PI. 72, figs. 75, 76. 
Shell lengthened-auriform, flat, subtranslucent, rather thin, con- 
centrically striated, whitish ; spire very short. _Whorls 4, the ear- 
lier 3 forming the spire, last whorl very ample. Aperture long- 
ovate, the margins separated, right margin somewhat incurved, 
flexuous, left margin prominent, acute, grooved outside above at 
the umbilical fissure. ( Guppy). 
St. Christophor (St. Kitts), West Indies. 
Haliotinella patinaria Guppy, Journal de Conch., 1876, p. 163; 
Journ. de Conch., 1878, p. 822, pl. 10, f. 1. Compare Morch, J. de 
C., 1876, p. 374. 
Morch considers this the shell of Plewrobranchus quadridens. 
Genus GYMNOTOPLAX Pilsbry, 1896. 
Similar, so far as known, to Plewrobranchus, but the mantle is 
partly open or perforate above, exposing part of the shell. This 
condition occurs in no other Pleurobranchide. 
G. AMERICANUS Verrill. Pl. 74, fig. 91. 
In alcohol the body is oblong, higher than wide, with the mantle 
extending over the greater part of the shell. The foot is large, 
thick, with short, rounded, grooved auricles in front, its lateral sur- 
faces, like those of the mantle, covered with small projecting spicules. 
Head bluntly rounded, with two broad, leaf-like oral tentacles and 
