TYLODINA. 185 
Hyalopatina rushii DALu, Blake Gastrop., p. 61 (1889). 
This remarkable shell has been some time in the National Mu- 
seum, and has been submitted to several conchologists, and studied 
with much care. In the absence of any further information, I have 
come to the conclusion that it may be related to Umbraculum, from 
which, conchologically, it is separated by its oval form, posterior 
nucleus, and granulated surface. The discovery of a living speci- 
men, however, may show the true relations of the creature to be 
elsewhere. It has a little the general appearance of an extremely 
thin, flat Crepidula wnguiformis without a deck, and with the nucleus 
within the margin (Dal/). 
The figure is from a drawing kindly lent by Dall. 
Genus TYLODINA Rafinesque, 1819. 
Tylodina Rar., Analyse de la Nature, ou Tabl. de Univers et 
des Corps Organises, 1815, p. 145 (nude name) ; Journal de Physique, 
de Chimie, d’Hist. Nat., ete., Ixxxix, p. 152 (1819).—Joannisia 
Monrerosato, Nomencl. Gen. e Spec. Conch. Médit., p. 149 (1884), 
type T. citrina. 
Animal almost completely retractile under the shell; foot flat, 
broadly truncate in front, pointed behind; head distinct, elongated 
and sub-bifid in front, with a buccal veil terminating in labial ten- 
tacles, the mouth between buccal veil and foot; dorsal tentacles 
long, cylindrical, slit on the outer sides almost their entire length, 
with olfactory lamellee within the slit. Eyes sessile at their interno- 
anterior bases; mantle completely covered by shell, its edge den- 
ticulate. Branchial plume bipinnate, free for the greater part of its 
length, lying between mantle and foot on the right side, the end 
projecting backward. Anus behind the gill; genital pore in front 
of gill. 
Radula armed with many similar narrow teeth; jaws rudimen- 
tary ; gizzard with numerous corneous denticles. 
Shell external, conical and limpet-like, calcareous except at the 
borders which are membranous ; apex recurved, when perfect com- 
posed of two glossy, vitreous whorls, coiled spirally to the left and 
backward. 
Distribution: Mediterranean, Gulf of Mexico, California. 
This genus differs notably from Umbraculum in having the shell 
larger in proportion to the body, in the projecting head, not included 
in an anterior sinus of the foot, and in the external genitalia. 
