1896.] NATURAL SCIENCES OF PHILADELPHIA. 339 



REVISION OF THE NORTH AMERICAN SLUGS: ARIOLIMAX AND 



APHALLARION. 



BY HENRY A. PILSBRY AND E. G. VANATTA. 



The genera of slugs inhabiting North America have hitherto 

 been discriminated by external characters, and those of the jaw and 

 teeth. We purpose to indicate, in a series of papers of which this 

 is the first, some of the more important of their internal features, 

 particularly the genitalia and alimentary canal. 



The genitalia have been utilized by Mr. W. G. Binney and others 

 for the discrimination of species ; and we have already considerable 

 knowledge of these organs from his descri{)tions and drawings; but, 

 of late, quite a new stress has been laid upon certain characters of 

 the organs of generation. By Dr. Simroth, in Germany, and the 

 senior author of this paper in America, characters of generic, as 

 well as of still higher value, have been found in the genitalia. It 

 is, therefore, important to review our data upon the anatomy of 

 American slugs, to correct the numerous misinterpretations of organs 

 which have arisen from lack of good material or other causes, and 

 to expose the true generic characters and affinities of these animals, 

 so far as may be possible in the present state of our knowledge. 



As the species of slugs also rest largely upon characters of internal 

 anatomy, their revision will be attemjjted ; a work now most timely, 

 in view of the fact that such a multitude of insufficiently defined 

 specific and varietal names have been proposed that he who attempts 

 the identification of a West Coast slug to-day is not only a bold 

 man but also one probably doomed to a miserable failure. 



The largest slugs of America, Ariolimax and Aphallarion, are 

 selected for the present essay. 



No correct figures or descriptions of the genitalia of these animals 

 have yet been published. The true structure of the male organs of 

 Ariolimax is here for the first time made known ; and the genus 

 Aphallarion is proposed for a new species, perhaps the largest Amer- 

 ican slug, remarkable in lacking a penis.^ 



^ We must acknowledge our indebtedness to P. B. Kandolph, of Seattle, 

 Washington, and to Fred L. Button, of Oakland, California, for large series 

 of slugs used in preparing this paper. 



