Boone, Mollusca, Cruises of "Eagle" and "Am," 1921-28 187 



Distribution: "West Indian region: Honduras; Swan Island; 

 Royal Isle Harbor. 



Material Examined : Two specimens, captured in Turtle Harbor, 

 Florida, by the "Ara." 



Color : Unrecorded. 



Life History : Unrecorded. 



Technical Description: Body subcylindrical, tapering poster- 

 iorly bluntly rounded distally ; anteriorly the free edge is produced to 

 a slight blunt triangular point in the median dorsal line, on either side 

 of which it tapers towards the lateral margin ; on the ventral surface 

 it is produced into a rounded point on either side of the siphon and 

 is concave between these points. The caudal fins begin a short dis- 

 tance behind the mantle edge, about 5 mm., and they are widest in 

 the middle, tapering toward each extremity, but a trifle more so near 

 the posterior end ; the free margins of the fins are very convex ; consid- 

 ered together, the fins and body form a long oval, broadest in the mid- 

 dle. The head is large, much wider than long, flattish dorsally, some- 

 what rounded laterally and with a deep triangulate depression on the 

 ventral surface, into which the dorsal surface of the siphon fits. Pos- 

 teriorly the dorsal margin of each is produced into a decided ridge, 

 diverging from a truncated point in the median region into an arc on 

 each side, which terminates behind the upper margin of the eye. Be- 

 hind this ridge the head narrows abruptly to the body. One either 

 side of the head the marginal ridge is less sharply defined but dis- 

 tinct, and behind it there is a wide, thin, broadly rounded laminate 

 membrane which bears on either side of its outer surface a cap-like 

 concavity. The eye is large, with prominent pupil in the dead 

 specimen. 



The outer buccal membrane is well developed with its outer mar- 

 gin produced into six acute points, the lower three of which are the 

 larger ; one point extends between the two dorsal arms ; one each be- 

 tween the dorsal and upper lateral arms ; one between the margin of 

 the lower lateral arm and tentacular arm and the sixth point occurs 

 between the two ventral arms. The exposed surface of the buccal 

 membrane is rough on the upper half, and on the lower is furnished 

 with numerous closely set, fleshy, tapered hook-like, soft-bodied, ten- 

 tacle-like processes. The inner margin of the buccal membrane closely 

 surrounds the beak and is very muscular. The lower mandible has a 

 strong upcurved beak, into which the upper mandible fits. 



