i6o Transactions of the Royal Canadian Institute 



27.5 mm. The largest living specimen I have noted was 30 mm. long by 

 15 broad by 6 high but some preserved specimens must have been larger 

 than this though none appear more than 40 mm. long. 



Head. — The head is small, quite hidden by the mantle and bears 

 laterally a pair of digitiform tentacles about 1.5 mm. long. The mouth 

 is a small longitudinal slit. 



Foot. — The foot is narrow elongated oval; the front end is sharply 

 rounded off and the hinder end comes to a blunt point. It is bilabiate 

 anteriorly and the thin upper lip has a slight median notch. 



Rhinophores. — The rhinophores can be completely withdrawn into a 

 deep sheath with a crenulate edge. They are sub conical with a dilated 

 perfoliate clavus bearing 20-30 leaves. 



Branchiae. — The six tripinnate plumes are in nearly a complete circle 

 around the anal papilla and can be entirely withdrawn into a sheath with 

 a slightly crenulate margin. The anal papilla is large while the renal 

 aperture lying in front and to the right of it is small and inconspicuous. 



Radula. — The radula is yellow, fairly deeply grooved short and broad. 

 The teeth are arranged in 19-22 rows each half row containing from 25- 

 30 teeth. The rachis is broad and naked. The teeth are flattened and 

 strongly curved; the innermost two or three small, the following ones 

 larger and diminishing again to the edge. 



The glans penis is well developed, unarmed but covered with thin 

 cuticle. 



A short description of the external features of this species was given 

 by Cooper, later the internal anatomy was dealt with by Bergh in forms 

 from Alaska. 



Habitat. — It is fairly common in the neighbourhood of Departure Bay 

 on rocks and in pools during April, May and June. Specimens have been 

 taken from the Lagoon near Hammond Bay, Jesse Island, False Narrows, 

 Mudge Island and dredged in Northumberland Strait (Station 5) and 

 other places. This form has been recorded from various places on the 

 Pacific coast of North America: Sitka, Unalaska, Puget Sound, Monterey 

 Bay, Santa Barbara, San Diego and a light coloured variety (var pallida) 

 is recorded by Bergh from Punta Delgada off the coast of Patagonia. 



I feel inclined to doubt strongly the validity of this var pallida as 

 given by Bergh (3, p. 172). It was founded on three specimens preserved 

 in alcohol, the main difference being that of colour. That author says 

 "Trotz dem Fehlen der bei anderen Individuen gesehenden dunkeln 

 Ringen stelle ich, vorlaufig wenigstens, diese Form als eine helle Varietat 

 der Diaulula Sandiegensis hin". The preservation of the colour of most 

 nudibranchs is subject to great variation dependent among other things 

 apparently, upon the preservative used, its strength, amount of subse- 



