REPOET ON THE HOLOTHUEIOIHEA. 
53 
C. Deposits — reddish-brown, concentric bodies alone. 
Trochostoma ooliticum [Chirodota), Pourtales, 1851; Danielssen and Keren, 1878, 1882. 
Holoth uria imitactes, Gould, 1841 (according to Pourtales) . Molpadia oolitica, 
Selenka, 1867 {partim). Haplodactyla oolitica. Semper, 1868 {partim). 
EaUtat . — Massachusetts at Boston (Gould, Pourtales, Selenka), Block Island south of 
Cape Cod, and Boon Island (Yerrill). 
Neither in the papers of Danielssen and Koren and Sars, nor in those published by 
Pourtales, have I found any direct statement of the conformation of the tentacles 
in Trochostoma horeale and Trochostoma ooliticum; but Danielssen and Koren, who 
refeiTed these species to Trochostoma, distinguish the named genus from Haplo- 
(lactyla, by its having digitate tentacles and the integument mostly rough. Por 
my own part I do not believe these characters to be of much importance, and 
the more so as several species of Trochostoma have very rudimentary digits, 
evidently forming a transition to Haplodactyla with its simple tentacles, and, 
besides, two species of Trochostoma have the skin smooth. Further investiga- 
tions may prove whether the specific characters above cited be true, or only of 
varietal significance, or due to difference of ages or sex. 
D. Deposits in the perisoma, absent. 
Trochostoma arenicola (Liosoma), Stimpson, 1857. 
Habitat . — San Pedro in California (Stimpson). 
Each of the fifteen tentacles “ is composed of a short peduncle with four or five digita- 
tions at the disk -like summit.” With regard to the deposits, Stimpson says : 
“ The genus differs from Chirodota in the want of the calcareous deposits in the 
skin so characteristic of the later form.” Numerous specimens of a Trochostoma 
are preserved in the State Museum of Stockholm, dredged at the same locality in 
California, which, in external appearance, are almost like the preceding northern 
species, and donbtless are just the same forms as that examined by Stimpson. 
They are of about the same body-form as, for instance, Trochostoma horeale and 
Trochostoma arcticum, &c., but possibly more swollen at the middle of the body. 
They resemble the above named species in internal and external organisation, 
but seem to be totally devoid of deposits in the perisome. The tentacles are 
completely retracted in all specimens, consequently it is not possible to state 
their true appearance, but they evidently bear some short digits. Integument 
thick, smooth, leathery. Calcareous ring with five bifurcate prolongations 
posteriorly. The retractors absent, but traces of such present where the longi- 
tudinal muscular bands join the calcareous ring. 
