PLEUROBRANCHUS AGASSIZII MAC FARLAND 67 



a deep median notch. Its length is 24.0 mm., the width 12.0 mm. 

 The ground color of the foot is pinkish, thickly set with irregular 

 brownish blotches, apparently arranged at random, i. e. producing 

 no definite color pattern. The largest of these blotches may 

 reach a diameter of i.o mm., but the majority are much smaller. 



Head. The head is retracted and bears two tapering 

 conical oral tentacles, 2.5 mm. long, and with a basal diameter of 

 i.o mm. 



Rhinophores. The rhinophores are completely retracted 

 within their sheaths, the margins of which are low and closely 

 set with short slender papillae. The clavus of the rhinophore is 

 stout, club shaped, and lamellate. 



Branchiae. The branchiae are situated as usual upon the 

 posterior mid-dorsal region, surrounding the anal papilla and the 

 renal opening. They are six in number, tripinnate, and retractile 

 within a deep branchial pocket, the margin of which is thin and 

 slightly prominent. 



Total length of the specimen 32.0 mm., its width 12.0 mm. 



INTERNAL ANATOMY. 



The dorsal wall of the body cavity is rather firm and thick, 

 its peritoneal lining colorless, save for a pinkish tint, which is 

 possessed by all the viscera in common. 



ALIMENTARY SYSTEM. 



The alimentary canal is of the general type of the crypto- 

 branchiate Dorids. The pharyngeal bulb is conical, truncate in 

 front, 3.5 mm. long, by 2.5 mm. wide, and 3.0 mm. in height, the 

 radula sheath projecting behind and below as a rounded eminence. 

 The mouth opening is of an inverted T shape, the labial disc 

 being covered by a firm transparent cuticle. 



Labial armature. Externally the opening is guarded on 

 either side by a somewhat triangular, yellow plate, the apex of 

 which is directed backward (PI. XII, fig. 58). The anterior 

 border of each of these labial plates is slightly convex, ca. 0.8 1 mm. 

 long, the upper border is straight, 0.72 mm. long, and is separated 

 from its fellow on the opposite side by a distance of from 0.05 to 

 0.06 mm. The posterior border is very slightly concave, 1.08 mm. 

 in length, while the lower angle is rounded. 



