NATURAL SCIENCES OF PHILADELPHIA. 191 



lingual membrane. I regret not being able to give more accurately 

 the characters of the individual teeth,' but have lost the membrane 



Fin. 38. 



Lingual dentition of S. incnna. 



in removing it for examination. There are 129 rows of 24 — 1 — 24 

 teeth each. See Proc. Ac. Nat. Sc. Phila., 1874, pi. VIII., fig. 1, 

 for figure of dentition of S. decumana. 



(3) Jaw with decided short, vertical ribs to its anterior surface. 

 Genus ARION, Fer. 



I have not been able to give any information regarding two spe- 

 cies found within our limits, A. Andersoni (see below, p. 194), and 

 A. foliolatus. Indeed there seems so much uncertainty in regard 

 to them, that I doubt their belonging to this genus. For fuller 

 information, see Ann. N. Y. Lye. of N. H., X. 29t. This leaves 

 only one species, A. hortensis, Fer., described and figured in Terr. 

 Moll. IT. S., and in L. and Frw. Sh. N. A., I., referred to A.fuscus, 

 Mull. 



The species was introduced by commerce into Boston many 

 years ago. It still exists there,'^ specimens having been found by 

 me in 1871, from one of which I extracted tlie jaw and lingual 

 membrane here described. I have compared the figures of the 

 genitalia of A. hortensis given by Lehmann and A. Schmidt* with 

 those given by Leidy in Terr. Moll. U. S. There is a diff'erence 

 in the position of the retractor muscle of the penis. Leidy places 

 it at the base of the penis sac, Lehmann at the top, Schmidt omitting 



' Too late for illustration in the text, I have received specimens collected 

 by Mr. W. W. Colkett at Key West. There are 27—1—27 teeth, of the 

 same type as in P. decumana, referred to in the text. 



2 Specimens can readily be found in gardens between Chestnut and Mt. 

 Vernon Streets above Willow Street, as well as elsewhere. 



3 Der Geschlechtsapparat der Stylomraatophoren, 1855. 



