ARTICLE VI. 
ON THE NUDIBRANCHIATE GASTEROPOD MOLLUSCA OF THE NORIH 
PACIFIC OCEAN, WITH SPECIAL REFERENCE TO THOSE OF ALASKA. 
BY DR. R. BERGH, COPENHAGEN. 
PART: If. 
DIAULULA, Beh. 
Diaulula, Beh., Malacolog. Unters. (Semper, Philipp. II, ii), Heft xiii, 1878, 
p. 567; Heft xiv, 1878, p. xxxv. Gattungen nordischer Doriden, Arch. 
f. Naturg., xxxv, 1, 1879, p. 343. 
Forma corporis subdepressa. Dorsum minutissime villosum, holo- 
sericeum, molle. Tentacula digitiformia. Apertura branchialis ro- 
tundata, crenulata; folia branchialia tripinnata. Podarium antice 
bilabiatum, labio superiore medio fisso. 
Armatura labialis nulla. Lingua rhachide nuda, pleuris multiden- 
tatis, dentibus hamatis. Prostata magua; penis inermis. 
In their general form the Diaululx! somewhat resemble the Disco- 
dorides and the Thordise,? although their habitus still is peculiar. 
The back is villous, as in these genera and especially as in the Thor- 
disez, but finer and more velvet-like. The tentacles are finger-shaped, 
smaller than in the Discodorides, larger than in the Thordise. The 
branchial-slit is rounded, crenulated; the branchial leaves tripinnate. 
The anterior margin of the foot bilobed, the upper lip broader, with a 
median fissure. As in the Zhordise, there is no armature of the 
lip-disk. The radula nearly agrees with that of the Discodorides; 
the rhachis is naked; on the pleure there is a rather broad series of 
plates of the usual hook-shape. The stomach is enclosed in the liver 
(not free, as in the Discodorides and in the Thordisx). As in the 
Discodorides, there is a large prostate and an unarmed penis. 
Only the following species appears to be hitherto known, from the 
northern Pacific. 
1. D. Sandtegensis (Cooper). 
1 Diaulus, medicus, cf. Martialis, I, 48, p. 40. 
* Cf. my Malacolog. Untersuch. (Semper, Pun TI, ii), Heft xii, 1877, 
p. 518, (Discodoris) ; p. 540 ( Thordisa). 
(189) 
