OPISTHOBRANCHIATA FROM THE ABROLHOS ISLANDS. 531 
they have a very thin crenulated edge along their basal portions. The teeth 
decrease in size rapidly at the margin, and the last one or two consist oi: a 
single elongated basal plate with no spine. 
The conspicuous genital aperture is to be found just in front of the aiiterior 
edge of the mantle to the right of the middle line. The seminal groove is 
well marked and passes forward around the outside of the right rhinophore 
to the penis underneath the right cephalic tentacle. 
The anus lies on a fold of the mantle to the right of the middle line behind 
the visceral hump. In this region the mantle is somewhat thickened and 
produced to form an anal funnel which projects beyond the pleuropodia. 
Notes. Two specimens were obtained from near Fremantle (some 250 
miles south of the Abrolhos region), and as Sowerby's specimens were 
also from "Swan River" the present ones can probably be regarded as 
topotypes. 
Species Tethys denisoni (Smith), Rep. Zool. Coll. 'Alert,' p. 89 (1884). 
(PI. 27. fig. 2 ; PI. 29. figs. 23-25.) 
Body. The body is plump, high, and somewhat egg-shaped, being wider at 
the hinder end than at the front end, and it passes forwards into a narrower 
heiid or cephalic region. The visceral hump appears to be thiown rather far 
back as compared with T. {Aplysia) punctata. The pleuropodial lobe^ arise 
laterally about as far behind the rhinophores as those are behind the oral 
tentacles ; they are moderately large and freely separable. Posteriorly they 
unite and form a sort of transverse flange across the hinder end of the body 
above the caudal prolongation of the foot. The mantle covers the shell, but 
possesses a small central perforation, and it also largely covers the ctenidium, 
which is free for a short distance at ifs postero-lateral end. The anal funnel 
is well developed. The integument covering the whole animal is ve^rj 
smooth, but thrown into wrinkles. 
The opaline gland is a well-defined body lying under the right anterior 
portion of the mantle and opening to the mantle by a single fairly large pore 
and not by a series of apertures as in the European T. punctata. 
Colour. When preserved thts animals are of a pale greyish white and the 
wrinkles are often black, very similar to those in 2\ gigantea. Professor 
Dakin informs me that in life they are of an olive-green colour with some 
darker mottlings. 
Dimensions. The largest specimen when preserved measured 6 cm. long- 
by 3 cm. wide and 3"2 cm. high. 
Head. This may be regarded as including the head and neck. The mouth 
is terminal and takes the shape of a vertical slit; on each side is a fairly 
large auriculate tentacle. These pass down on each side of the mouth, and 
at their upper border are curled round to form a groove directed posteriorly 
and outwards. They are separated in the mid-dorsal line and show no 
3a* 
