1 66 Transactions of the Royal Canadian Institute 



dorsum is marked off from the sides by a low ridge which bears five 

 characteristic processes and continues on in the line of the edge of the 

 veil. Each process is about 3-4 mm. long and slightly curved inwa;rds 

 over the back. The inner surface of the process is smooth while the 

 outer bears a double series of small blunt papillae and the top of the 

 process is a rounded opaque knob. These processes are all about the 

 same size and do not decrease noticeably towards the hinder end. The 

 dorsal ridges disappear behind the last dorsal process leaving the animal 

 with a sort of bluntly rounded tail. The sides of the body are almost 

 upright and slightly convex; they are smooth save that in one specimen 

 they have 4 or 5 tiny blunt papillae and are marked off from the foot by 

 a small ridge like fold. 



Colour. — The general body colour is translucent white or very pale 

 yellowish white. The knob-like terminations of the dorsal processes are 

 opaque and of a more decided yellow colour or even orange red. The 

 back and the sides bear a number of tiny brownish spots most of which 

 are quite tiny and also some reddish spots which are larger. They are 

 more plentiful at the front and thin out behind the branchiae and finally 

 there is a group of small ones at the end of the tail. The same dull Hght 

 brownish colour tinges the branchiae, the papillae on the frontal veil 

 and the clavus of the rhinophores. The branchiae and papillae of the 

 frontal veil may be tinged with orange red. 



Dimensions. — ^The largest living specimen examined measured 40 mm. 

 long 10.5 mm. wide and 8 mm. high. 



Foot. — ^The foot is elongated and fairly narrow with approximately 

 parallel sides running off to a point posteriorly and bluntly rounded 

 anteriorly. 



Head. — The head is rounded and bears a transverse slit-like mouth. 

 On each side is a short auriform oral tentacle with a well marked groove 

 on its outer border. 



Rhinophores. — ^The rhinophores are completely retractile into cylin- 

 drical sheaths which project up above the dorsum and have a slightly 

 wavy margin. They lie just inside the dorsal ridge at the level of the 

 hinder end of the veil. The perfoliate clavus is blimtly conical and bears 

 about 20-25 leaves. It is borne upon a stout cylindrical stalk. 



Branchiae. — The branchi(al plumes are five in number in all specimens 

 save one, where a sixth is present and incompletely retractile. They 

 have regular tripinnate branches and are entirely separate at the base. 

 The anterior plume is median, the remaining two pairs are lateral and 

 in the space between them lies the anal cone with a tiny renal pore at 

 its base on the right side. 



Radula. — -The raduia is composed of 20-22 rows. There are four 



