40 PROCEEDINGS OF THE ACADEMY OF [1880. 



ON THE NUDIBRANCHIATE GASTEROPOD MOLLUSCA OF THE NORTH 

 PACIFIC OCEAN, WITH SPECIAL REFERENCE TO THOSE OF ALASKA. 



BY DR. R. BERGH, COPENHAGEN. 



PART II. 



DIAULULA, Bgh. 



Diauhila, Bgh., Malacolog. Unters. (Semper, Philipp.II, ii), Ileftxiii, 1878, 

 p. 567 ; Heft xiv, 1878, p. xxxv. Gattungen nordischer Dorideu, Arch. 

 f. Naturg., xxxv, 1, 1879, p. 343. 



Forma corporis subciepressa. Dorsum minutissime villosum, holo- 

 sericeum, molle. Tentacula digitiformia. Apertura branchialis ro- 

 tundata, crenulata ; folia branchialia tripinnata. Podarium antice 

 bilabiatum, labio superiore medio fisso. 



Aimatura labialis nulla. Lingua rhachide nuda, pleuris multiden- 

 tatis, dentibus hamatis. Prostata magua ; penis inermis. 



In their general form the Diaidulx^ somewhat resemble the Disco- 

 dorides and the TJwrdisee,'^ although their habitus still is peculiar. 

 The back is villous, as in these genera and especially as in the Thor- 

 disse^ but finer and more velvet-like. The tentacles are finger-shaped, 

 smaller than in the Discodorides, larger than in the Thordisse. The 

 branchial-f-lit 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 Thordisse^ there is no armature of the 

 lip-disk. The radula nearly agrees with that of the Diacodorides; 

 the rhachis is naked ; on the pleurae 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 Thordisse). 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. Sandiegensis (Cooper). 



^ Diaulus, medicus, of. Martialis, I, 48, p. 40. 



* Cf. my Malacolog. Untersuch. (Semper, Philipj^ II, ii), Heft xii, 1877, 

 p. 518, iDiscodoris) ; p. 540 {Thordisa). 



