TERENNOPHORUS. 179 



small, inner cusp, bearing a small conical cutting point, and another, outer, 

 larger cusp, bearing an extraordinarily developed, wide, expanding, bluntly 

 truncated cutting point. As the teeth pass outwards towards the outer margin 

 of the membrane, they at first increase and then decrease in size, but retain 

 the same shape quite to the edge. 



The dentition of several Eastern species has also been published. 



The Onchidiidce are described as agnathous, but I am confident of having 

 observed the jaw figured. I found none in Onckidium Schrammi (see Ann. 

 Lye. Nat. Hist, of N. Y., X. 339). 



Onchidella borealis, DALL. 



Animal small, black, with dots and streaks of yellowish white, foot light 

 colored, also muzzle and tentacles. Back regularly rounded, but a little 

 pointed in the middle ; smooth or very finely granulose, tough, and coriaceous. 

 Eyes globular, blue, on very short constricted tentacles. Muzzle short, 

 rounded-transverse. Head not produced beyond the anterior edge of the 

 mantle. Sexual appendages on the right side, near the head. Foot ovate, 

 narrow, rather roundly pointed behind. Lon., .3 in. Hal. Sitka, Alaska Ter- 

 ritory, on the rocks near tide-marks, especially on the small islets in the 

 Bay. (Dall.) 



Onchidella borealis, DAT.L, August, 1866, Am. Journ. Conch., VII. 135. 



Found from Prince William's Sound to Vancouver's Island, by Mr. 

 Dall, to whom I am indebted for specimens, one of which is figured on 

 p. 178. 



For jaw and lingual membrane see above. 



TEBENNOPHORUS, BINN. 



Animal limaciform. Body somewhat flattened, terminating obtusely, or in a 

 somewhat truncated form, obtuse anteriorly. Back convex, more flat when 

 fully extended. Integuments with irregular vermiform glands, anastomosing 

 with each other, and having a general longitudinal direction. Mantle covering 

 the whole body. Foot expanded at its margin, and visible beyond the sides of 

 the mantle; no locomotive disk. Respiratory orifice near the head, some way 

 to the rear of the right oye-peduncle. Anal orifice contiguous Fi gg 

 to, and a little above and in advance of the pulmonary orifice. 

 Orifice of organs of generation behind and below the right 

 eye-peduncle. Without terminal mucus pore. No external or 

 internal shell. 



Jaw horn-colored, arcuate, with irregular concave margin, 

 beating a blunt, slightly projecting beak ; terminations blunt ; the anterior sur- 

 face convex, without a decided median carina, and strongly striate. 



The genus is not peculiarly American, as it is also found in Asia. In North 



