1896.] NATURAL SCIENCES OF PHILADELPHIA. 343 



grooves, deeper toward the more or less distinct caudal mucus gland. 

 Mantle oval, about one-fourth as long as the entire body, finely 

 granular, the respiratory orifice at its posterior third near the right 

 edge. Genital orifice behind the right eye tentacle. Orifice of the 

 suboral gland very broad. Integument scored by numerous grooves, 

 longitudinal behind, obliquely descending below the mantle and for 

 some distance along the flanks.^ Sole tripartite, the divisions rather 

 indistinct ; alcoholic specimens having the median band smooth, 

 lateral bands finely transversely wrinkled. 



The principal internal characters of the genus are mentioned 

 above. The extraordinary modification of the penis is fully de- 

 scribed below. 



Key to species of Ariolimax. 



a. jVtantle free anteriorly for about one-third of its length. Penis 

 with terminal retractor, and nearly filled for its entire length by 

 the invaginated epiphallus; vas deferens not enlarged, 



ColumbictJius. 

 aa. Mantlefreeanteriorly about one-fourth of its length. Penis hol- 

 low, with very broad retractor, beyond which it is attenuated; 

 vas deferens enlarged into an epiphallus external to the penis, 

 the invaginated portion small. Californicus. 



A. Columbianus Gould. Plate XII, fig. 2. 



Li77iax Columbianus Gld. in Terrestrial Moll. U. S., II, p. 43, pi. 66, f. 1 

 (1851); U. S. Expl. Exped., Moll., p. 3, pi. 1, f. 1 (1852); Tryon, Amer. 

 Jour. Conch., Ill, p. 315 (1868). 



Ariolif?iax Columbianus Morcli, Malak. Blatter, VI, p. 110 (1859). W. G. 

 Binney, Amer. Journ. Conch., I, p. 48, pi. 6, f. 11-13; Land and Fresh 

 Water Sh. N. A., I, p. 279, f. 496-501, (1869); Proc. Acad. Nat. Sci., 

 Phila., 1874, p. 33, pi. 2, f. B. to H; Terr. Moll., V, p. 231, pi. v, f. E (denti- 

 tion), pi. xii, f. C (genitalia) ; ]Man. Amer. L. Shells, p. 98, f. 58, 59, 6' ,"61 ; 

 Third Supplement to Terr. Moll., V (Bull. Mus. Comp. Zool., XIX, No. 4), 

 p. 211, pi. vi, f. A (mottled form) and f. G (penis). 



* Mr. Charles Hedley, the accomplished Australian student of mollusk 

 morphology, considers the oblique surface grooves as characteristic of the 

 ^utocopoda generally. I quote this passage from a recent letter: "Besides 

 the pedal grooves, tail pore and horn, the typically developed Aulacopod has 

 a keeled tail and oblique secondary grooves. The pore may be lost by de- 

 generation, so, too, may the oblique grooves ; and the keeled tail may become 

 flattened. Nevertheless, both are typical characteristics, and deserve mention 

 in the diagnosis. Again, the Holopoda have long tapering eye tentacles, with 

 bulbous tips, but the Aulncopoda have shorter cylindrical tentacles, less bulb- 

 ous at tip and set wider apart." 



There can be no doubt that the features mentioned by my friend are of very 

 frequent occurrence in the Aulacopoda, while they do not occur in Holopoda ; 

 but they are not invariable, the pedal grooves being, I believe, the only strictly 

 diagnostic external character of the group. — H. A. P. 



