6o OPISTHOBRANCHIATA OF BRAZIL 



inner and outer surfaces of the shell are quite smooth. The 

 length of the shell varies in the three specimens from 4.2 mm. to 

 5.5 mm., its width from 2.5 mm. to 3.0 mm. 



Foot. The foot is smooth, truncately rounded in front, more 

 pointed behind. No well marked pedal gland is visible at its 

 posterior end. The lateral margins of the foot are continuous, 

 undulating, the anterior margin bilabiate, the lower lip much 

 thicker than the upper, which bears a median notch. The dorsal 

 surface of the foot margin is smooth, with no visible pigmenta- 

 tion, if any existed during life. 



Head. The frontal veil is large, trapezoidal, its anterior, 

 free margin smooth, nearly straight, the outer angles very slightly 

 rounded, the external margin deeply auriculate. The width of 

 the frontal veil in the three specimens is 4.0, 4.0 and 3.0 mm. 

 respectively, the length being 1.5 mm. in all. The rhinophores 

 (PI. XII, fig. 57) are very large cylindro-conical organs, their 

 bases contiguous, but not fused. Each is made up of a loosely 

 rolled plate, the margins external, the lower one overlapping the 

 upper. The margins are prolonged at the base into a considerable 

 flap, which is free. Just above and external to the base the very 

 large eyes shine conspicuously through the integument. 



Ctenidimn. The branchial plume lies on the right side in 

 the roomy space between foot and mantle, completely concealed 

 by the latter. It measures one-half the total length of the body, 

 being 5.0 mm. long in the largest specimen, while in the smallest 

 one it is but 2.0 mm., i. e. one-fourth the body length. The 

 posterior half of the plume is free from the body wall ; the 

 rhachis entirely smooth. The plume is bipinnate, bearing about 

 twelve pinnules on each side, arranged alternately. The anal 

 opening is situated above the posterior end of the base of the 

 branchial plume. 



Internal Anatomy. 



Mandibles. The labial armature is made up of a pair of 

 oblong mandibles of a light amber color in their anterior portion, 

 becoming paler behind, borne upon the sides of the buccal open- 

 ing. Their greatest length is 1.215 mm., their width 0.66 mm., 

 being nearly twice as long as wide. The oblique anterior border 

 is slightly narrower than the more rounded posterior one, the dor- 



