NUDIBRANCHS OF THE VANCOUVER REGION 203 



orange and opaque white giving an iridescent effect so that a well marked 

 variety well deserves its specific name of opalescens. 



In spite of the colour differences that have been pointed out above 

 there is no doubt from its other features that it is the H. opalescens of 

 other authorities. 



Dimensions. — Cooper (5) gives the size of this animal as one and a 

 half inches and breadth a quarter of an inch and my own measurements 

 agree fairly well with this. The largest specimen measured 42 mm. long 

 by 12 mm. wide by 9 mm. high. 



Head. — The head is large, with a transverse slit-like mouth and its 

 margins are continued laterally into very well developed oral tentacles, 

 these are directed outwards and forwards in front of the head as much 

 as 18 mm. and are constantly in motion strongly recalling the "feelers" 

 of a snail. 



Foot. — The foot is well marked, elongated and somewhat lanceolate, 

 posteriorly it is pointed and anteriorly abruptly rounded. The front 

 margin is bilabiate, the upper lip thin and the lower one fleshy they bear 

 a shallow notch in the middle line. Both lips are continued out laterally 

 into short, slightly curved horn-like processes about 4 mm. long and 

 grooved on their antero -ventral border. In locomotion they are visible 

 from above. 



Rhinophores. — The perfoliate rhinophores are usually held erect and 

 turned slightly outwards. They are not retractile into a sheath and the 

 clavus occupying over half their length bears about 20-24 leaves. 



Radula. — The radula is long and narrow and curved in a slight spiral. 

 It bears from 25-27 large median teeth. Each tooth possesses a stout 

 median cusp on each side of which are from 4-6 small pointed denticles. 

 The under side of the central cusp is irregularly serrulate. 



Jaws. — The jaws are well developed, shell-like and of a yellow horn 

 colour. The masticatory edges are curved and their edges bear a row 

 of about 50 short, sharp denticles which increase in length as they pass 

 downwards and backwards, the hindermost being slightly serrulate. 



The penis is long and sub cylindrical when extruded and bears a 

 series of glandular nodules some distance from the end which are similar 

 to those in Facalana according to Cockerell and Eliot (4, p. 51). 



The species was first recorded by Cooper (5) and later Bergh (2) gave 

 a fuller account of it including its internal anatomy. It has been re- 

 ported from California by Cockerell and Eliot. 



Habitat. — This species is quite common in the neighbourhood and to 

 be found on the rocks above low tide level, at Jesse Island, Brandon 

 Island, Newcastle Island, Mudge Island, Round Island, False Narrows 

 and from the float at the Station. It has been recorded from Sitka in 



