14 Mr. W. H. Dall on certain 
which are more or less irregular in different individuals; faint 
yellowish areas seem to indicate a thin, very closely adherent 
epidermis ; apex prominent, more or less incurved and slightly 
laterally compressed, usually showing a scar where the em- 
bryonic nucleus was attached ; inside polished or smooth ; 
length 11:0, width 6°5, altitude 2°75 millim. Another dead. 
specimen is three times as large. 
Soft parts: Foot ovate, thin, not very high, somewhat 
pointed behind ; mantle-margin moderately wide, with a thick- 
ened plain border ; behind, on each side of the “ tail,” between 
the mantle and foot, is one cylindrical blunt filament; sinus 
above the head and neck quite deep; gill exactly as in Acmea, 
small, hardly projecting out of the sinus; head large, end of 
muzzle semilunate, with a strongly-marked margin; in the 
midst of this flat lunate area is a rounded papillose space 
surrounding the mouth ; this organ, if furnished with jaws at 
all, has them of such soft and cuticular consistency as to 
show neither under the knife nor under an ordinary dissecting 
microscope, but it appeared to be without jaws; tentacles 
moderate, subcylindrical; eyes none ; course of the intestine 
much as in Patella, but shorter. 
Dentition.—Rhachidian tooth squarish, rounded in front, 
nearly flat, about as long as the two inner laterals ; inner three 
laterals slender, with small denticulate cusps, outer or third 
usually a little longer than the others, but the proportions 
slightly different in the less mature part of the radula; fourth 
or major lateral about twice as long as the others and slightly 
broader than the rhachidian tooth, rather strongly cusped, the 
cusp notched into five or six denticles, and the shaft somewhat 
curved, the shaft and cusp translucent; uncini numerous (100 
or more), slender, slightly twisted and hooked, united on each 
side on a single continuous base, which is a little longer than 
the width of the radula between the uncini. 
Hab. Station 937 of the United-States Fish Commission 
in 1881. This is 102 miles S. by E. 4 E., by compass, from 
Gay-Head Light, Martha’s Vineyard, the bottom-tempera- 
ture being 40°-5 F., and that of the surface 72°-0 F. The 
same species was obtained by the United-States Coast-Survey 
dredgers on the steamer ‘ Blake,’ Lieut.-Commander J. R. 
Bartlett commanding, under the supervision of Prof. Alex. 
Agassiz, on hard bottom (temperature 44°°5 F.), at station 
288, in 399 fathoms, off Barbadoes, and off Martinique, in 
5024 fathoms sand and ooze, at station 195, bottom-tempera- 
ture 41°-0 F., the surface in both cases being about 80°-0 F. 
I take pleasure in naming this species after Mr. R. Rathbun, 
of the United-States Fish Commission. 
