84 TETHYS—WEST AMERICAN. 
calloused, but with no reflexed margin over the tip. Sinus short 
and very concave, margined. Surface smooth. Calcareous layer 
coextensive with the excessively thin, hardly apparent cuticle. 
Length 83, breadth 6 mill. 
St. Thomas (A. H. Riise; Dr. Hornbeck) ; St. Vincent (Guild- 
ing). 
Aplysia parvula Guitpine MS. in Morcu, Journal de Conchyli- 
ologie, 1863, p. 22; Mal. Bl. xxii, p. 176.—? A. rosea Rathkey 
Sows., Conch. Icon. f. 23 (1869). 
I have given Mérch’s very poor descriptions of the soft parts of 
this species, and have diagnosed and figured the shell from part of 
the original specimens received from Morch. It is unquestionably 
a distinct species, not closely allied to any other of the region. The 
shell is convex and solid, somewhat like Crepidula convexa Say in 
contour. The large oval orifice in the mantle is also a valuable 
distinguishing character, other described Antillean forms having 
this foramen minute or tubular. 
Whether the parvula of Morch is really Guilding’s mss. species is 
by no means certain; but fortunately there is no necessity for rais- 
ing the question. Sowerby has figured a shell from St. Vincent 
under the name A. rosea Rathke, which is the A. parvula of Guild- 
ing, according to him; but the real A. rosea was a Scandinavian 
species and in all reasonable probability a young punctata Cuv. 
III. Species of the West Coast of the Americas. 
a. Shell normal, with no accessory plate at the apex. 
b. Swimming lobes broadly united behind. 
c. Mantle excised behind, but with no tongue-like lobe. 
d. Mantle with a submedian perforation. Black, nigra. 
dd. Mantle with a large submedian oval orifice. Black- 
. ish, rangiana. 
ec. Mantle with a submedian perforation, and a posterior 
long, tongue-like siphonal lobe. Violet, with some white 
spots, blackish in alcohol, inea 
bb. Swimming lobes free to their union with foot behind. 
c. Mantle with a subcentral tube or papilla; swimming 
lobes very ample. 
d. Maculated ; opaline gland with one orifice, 
chierchiana, 
