626 PROCEEDINGS OF THE ACADEMY OF [Oct., 



A NEW AMERICAN GENUS OF ARIONID^S;. 



BY HENRY A. PILSBRY. 



Among other mollusks received from the Rev. E. H. Ashmun, 

 the fruits of his first season's collecting in Idaho, were a few small 

 slugs, about the size of Agriolimax campestris (Binn.). The dark 

 color, carinated tail and tripartite sole led me, upon first glance, to 

 think it an immature Amalia; but subseciuently, upon opening one 

 to confirm the identification, it became at once obvious that an Arionid 

 slug was before me — a slug not referable to any hitherto known 

 species. This slug shall be called Zacoleus idaJtocnsis. It is from 

 Meadows, Washington county, Idaho. ^ 



ZACOLEUS, gen. nov. 



The genus Zacoleus may be briefly defined thus: Ariolimacinse 

 with the penis a simple sac continued beyond the insertion of the vas 

 deferens; duct of the spermatheca enormously enlarged; marginal 

 teeth with very long zonitoid mesocones, no ectocones; intestine but 

 slightly twisted; sole tripartite; pneumostome behind the posterior 

 third of the mantle ; no caudal pore. Central nervous system peculiar 

 by the miusually long cerebral commissure and very short cerebro- 

 visceral and cerebro-pedal connectives. 

 Zacoleus idahoensis n. sp. 



Externally the slug is black on the mantle and back, the flanks and 

 head lighter, slate-colored; the neck or area around the anterior 

 border of the mantle is dirty wdiite. The reticulation is indistinct, 

 and longitudinal lines above, oblique on the sides, predominate, 

 somewhat as in Prophysaon cxruleum (CklL). Back of the mantle 

 the body is keeled, the tail strongly so. The foot-margin is rather 

 narrow. The sole is narrow, yellowish- white, and divided by longi- 

 tudinal grooves into three subequal areas. There is no caudal pore, 

 but the acute tail appears somewhat abruptly truncate posteriorly in a 

 view of the profile. The oval mantle somewhat exceeds one-third 

 the length of the body. The pneumostome is situated between the 



^ I am indebted to Mr. E. G. Vanatta for assistance in the examination of these 

 slugs. 



