NUDIBRANCHS OF THE VANCOUVER REGION 1 69 



form two triangular oral flaps. There is a slight notch at the front end 

 of the head. 



Foot. — The foot is well developed and has a slightly undulating 

 margin. At the front end it is broad and oval while at the hinder end 

 it passes off to a leaf- like tail. 



RhinopJwres. — ^The rhinophore is retractile within a low sheath with 

 a papillated margin. The stalk is cylindrical and the perfoliate clavus 

 is cylindro-conical with 22-24 leaves and slightly more than half the 

 length of the rhinophore. 



Branchiae. — The branchial plumes a,re 9 in number and not retractile. 

 They are arranged in the form of a horse-shoe with uncurved ends within 

 which is the low anal papilla and other papillae similar to those covering 

 the general surface of the dorsum. 



Radula. — The radula is long and narrow and folded into a deep 

 groove. It bears 26-28 rows of teeth each row composed of one large and 

 a series of 3-5 much smaller lateral teeth on each side. The base of the 

 large tooth is slightly longer relative to its breadth than in other members 

 of the genus I have examined and bears a large curved spine. The spine 

 is strengthened by a strong ridge which runs back well on to the basal 

 plate and bears a few irregular denticulations. These denticulations 

 are very variable even on the same radula and may be absent altogether. 

 The small lateral teeth are somewhat triangular in shape, weak and have 

 no well marked thickened ridge. They decrease in size as they pass out- 

 wards. Practically the whole length of the spine of the large tooth is clear 

 of the small ones. 



The lips are provided with a labial armature composed of a large 

 number of minute scales, some irregular and some trianglar in shape 

 arranged in the form of two curved leaf shaped plates. There is also a 

 ventral portion in the form of a curved plate forked anteriorly and ending 

 behind in a blunt point. 



The genital aperture lies high up on the right side just beneath the 

 mantle and behind the level of the rhinophores. The penis is sub-conical 

 and provided with minute hooks. 



The specimens agree most closely with those from Alaska described 

 by Bergh under the name Acanthodoris pilosa var albescens and only differ 

 in very small points. That author has also given a very complete 

 account of the species and its varieties. 



Habitat. — The specimens have been collected on the shore at False 

 Narrows and Mudge Island in May and also dredged near Horswell in 

 25 fathoms. It does not appear to be common. 



