34 PROCEEDINGS OF THE ACADEMY OP 



alcohol, and are evidently in various degrees of contraction. I 

 will say, however, that I found, in all the blind sac under the 

 mouth (well marked, though not very deep), which is suspected 

 by Dr. Leid}' to be the seat of the olfactory nerve. 



I can also here refer to several external characters not affected 

 or obliterated by contraction in alcohol. All the specimens have a 

 distinct locomotive disk to the foot. In all, the orifice of respi- 

 ration is decidedlj^ posterior to the middle of the right margin of 

 the mantle. The position of the anns I found in A. Golumbianus 

 to be posterior and inferior to the respiratory orifice, with a 

 gutter-like groove to the edge of the mantle. Tiie position of the 

 orifice of the generative organs is not so easily decided in alco- 

 holic specimens. I have no doubt, however, that in the living 

 animal it is under the mantle, not close behind the right tentacle. 

 In one form, Ariolimax Californicus, there are beyond doubt 

 two distinct orifices ; that of the male being smaller and anterior. 

 In Dr. Cooper's figure of A. Calif ornicus (Proc. Phila. Ac. Xat. 

 Sc. 1873, pi. iii. f. D 3) the two orifices are plainly shown, and 

 suggested to me the identity of my specimens with his species, 

 especially as the external markings also agreed with his descrip- 

 tion. In A. Golumbianus ? also there is no common duct or 

 cloaca, as Dr. Leidy calls it, to the genitalia, though I could not 

 detect more than one exterior orifice. In A. niger there can be 

 but one common orifice, judging from the penis entering into the 

 common cloaca, as shown in my fig. c of plate XI. 



The mantle is free on its margin in its whole circumference, espe- 

 cially in front and on its sides as far back as the respiratory orifice. 

 I could detect no concentric lines or other markings on the mantle. 

 The mantle was greatly produced and swollen on its margins in 

 Mr. Steam's specimen of A. Calif or Jiicus. In that and all the 

 specimens examined I found an internal shell, varying somewhat 

 in thickness, but always well marked, calcareons, subhexagonal, 

 longer than wide. In the specimen of A. Coluv^bianus '? there 

 were decided concentric lines of growth on the shell, as will be 

 seen in my fig. G, plate II. 



The caudal mucus pore was plainly visible in all the specimens 

 of ^. niger which I have examined. In fig. a of plate II. I have 

 figured the pore of this species. It seems to be in two portions, 

 one erect, triangular, at the end of the body of the animal, with 

 another running at right angles with it in a gutter-like excava- 



