NUDIBRANCHS OF THE VANCOUVER REGION 1 85 



outgrowth about hajf way down its outside border so that it simulates 

 the cerata. 



Cerata. — ^The cerata have a very characteristic appearance. They 

 rise from the sides of the dorsum as cylindrical processes which give off 

 branches, themselves to divide into smaller and smaller twigs. The whole 

 forms a delicate tree like structure which may be higher than the animal 

 itself. 



Radula. — The narrow pale yellow radula has about 45 rows of teeth. 

 The median tooth has an oblong base and a median spine, slightly 

 rounded at the tip and a little shorter than an equilateral triangle. Its 

 two edges each bear a series of about eightefen fine denticles extending 

 from near the tip right down to the shoulder. The lateral teeth are long 

 and narrow coming to a slightly curved claw-like end. The inner side 

 of the tooth is intact while the outer side bears at the end a series of 

 about 6 short spine-like denticles. The lateral teeth vary in number from 

 about 7-1 1. 



Jaws. — 'The jaws are strongly developed and take up a large part of 

 the side of the bulbus pharyngeus. They are in the form of a longish 

 oval hollowed plate rounded at the posterior end. Anteriorly they have 

 a median process mascatorius bearing several small teeth and having 

 just behind it the deepest part of the hollow. Above, the plate is con- 

 tinued as a curved somewhat narrow superior process. Below, the plate 

 bears a flange-like e;ctension, the crista connectiva by means of which it is 

 joined to its fellow. 



The penis is long and subconical with no armature. 



This species was n,amed by O. F. Muller and described in some detail 

 by Alder and Hancock (i) and again from Alaska by Bergh (2, 1879), the 

 former of whom give a complete synonymy. The latter author gave a 

 full description of D. purpureus but in a later paper (3, p. 139) says 

 "Der D. purpureus ist vielleicht nur eine dunkler gefarbte Varietat (of 

 D. arborescens) bei welcher noch dazu die Denticulation am Schneide- 

 rande der medianen Flatten schwacher ist und weniger weit hinaus an 

 der Spitze reicht". 



Habitat. — So far only two specimen^ of this form have been obtained ; 

 they were dredged from 15-20 fathoms near the Ballinac Islands (Station 

 51) July 29th, 1914. It is interesting as it is a species widely spread in 

 European waters and on the Atlantic coast of N. America. It has been 

 recorded by Bergh from Knohdoubin Isla,nd, Bristol Bay and near 

 HagemeJster Island in Alaska and ap D. purpureus from off Port MoUer 

 on the N. coast of Alaska peninsula. The present record extends the 

 southern limit of the species. 



