162 A MANUAL OF AMEiaCAN LAND SHELLS. 



tinct locomotive disk, though the reflection of the mantle on either 

 side of the foot gives a tripartite appearance to the under surface of 

 the body. 

 Shell none. 



In three specimens of 0. borealis examined I found a jaw (Fig. 148), 

 low, wide, slightly arcuate, ends scarcelj^ attenuated, blunt, anterior 

 surface ribless. 

 Lingual membrane (Fig. 149) long and wide. Teeth about 61-1-61, 

 ^^'■' ^^^ - arranged strongly eji chevron. The central tooth is large, 

 ^^^^^^Ifck longer than wide, truncated above, expanded below its 

 Jaw of o. borealis. middle and incurved at the basal margin. The reflection 

 is large, tricuspid, each cusp bearing a decided cutting point. The side 

 teeth are razor-shaped; they have a long, narrow base of attachment, 

 a small part of its upper portion thrown outwards, the balance curving 

 inwards, giving an irregular bow- shape to the whole base of attach- 

 ment, whose upper and lower edges are abruptly truncated. The re- 

 riG^i49. flection is near the base, and consists of a very small 

 inner cusp, bearing a small conical cutting point, and 

 another outer, larger cusp, bearing an extraordinarily 

 developed, wide, expanding, bluntly truncated cutting 

 Lingual dentition point. As the teeth pass outwards towards the outer 



of O. borealis. -• '- 



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 were formerly described as agnathous, but I am con- 

 fident of having observed the jaw figured. I found none in OncMdium 

 Schrammi (see Ann. Lye. Nat. Hist, of N. Y., X, 339) nor in Onchidella 

 Carj>enteri (see below). 



Onchidella borealis, Daxl. 



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 granulous, tough 

 and coriaceous. Eyes globular, blue, on very short constricted ten- 

 tacles. Muzzle short, rounded -transverse. Head not produced beyond 

 the anterior edge of the mantle. Sexnal appendages on the right side, 

 near the head. Foot ovate, narrow, rather roundly pointed behind. 

 Lon., .3 in. 



