36 Nils Hj. Odhner. 
rounded, posterior end slightly thickened and prolonged rear- 
wards into a tapering point; this prolonged terminal lap covers 
the cloacal cavity, which is closed inferiorly by the involuted 
margins of the same lap (fig. 55). Mouth subterminal, indistinctly 
separated from the ventral furrow. The latter is narrow, contains 
1 or 3 longitudinal folds (in different sections) and is separated 
from the cloacal cavity by an invagination. 
Cuticula very thick, composed of 4—5 layers (fig. 58) of 
needle-shaped hollow spicula, which are all tangential and cross 
each other in two directions almost at right angles (fig. 56); only 
the sides of the ventral furrow are bordered with erect spicula. 
Radula polystichous but divided longitudinally by a median 
furrow (fig. 57), with more than 30 transverse series, each con- 
taining about 16 teeth all having long, slightly curved, cusps and 
broad thin basal plates; the central teeth smaller, the lateral ones 
larger. Ventral salivary glands opening above the radula and 
much prolonged rearwards, about 15 times longer than the 
breadth of body. 
Dorsal coecum of the intestine penetrating beyond the brain 
in front. Shell gland with the paired proximal portions widened 
to an unpaired median ampulla. 
Colour (in alcohol) grayish or brownish white. Maximal 
length (according to KOREN & DANIELSSEN) 70, breadth 3 mm. 
The above diagnosis expresses the essential characteristics of 
the present species and the chief points in which it differs from 
D. acuta HEATH, hitherto known as the sole species of the genus.) 
I give below a more detailed description of its anatomy, from 
which it is evident that in other respects a very perfect agreement 
exists between the two forms. 
In the cuticula the epidermis papillae have the narrow shape 
and the relatively remote arrangement which is shown in HEATH'S 
figure of D. acuta (1911, pl. 33, fig. 4). Beneath the cuticula 
two muscular layers follow: a circular externa] and a longitudinal 
internal one. No sensory organ was to be observed externally 
on the dorsal side of the posterior end of the animal. 3 
In a transverse section through the median part of the body 
the following organization was observed: 
In the intestine the dorsal wall which covers the gonads is 
thinner than that of the remaining parts and is constituted by a 
1) In 1918 HEATH has described a third species, D. peroneopsis, from 
Martha’s Vineyard. 
