164 On the Systematic Arrangement of 



with a beak-like median projection to its cutting edge. Lin- 

 gual membrane, with separated, conical, aculeate marginal 

 teeth. 



Genus Hyalina (p. 29). — We have already stated our 

 views relative to the value of the caudal mucus pore as a 

 family character, and in consequence unite the Arionidoe to the 

 Ilelicidce. This brings the genus Zonites next to the genus 

 Hyalina. The two genera are very nearly allied, their only 

 distinction, so far as known to us, being in the presence in 

 Zonites of a distinct locomotive disk to the foot, and of 

 longitudinal furrows along the side of the animal near its 

 base, rising over the top of the tail and uniting above a ter- 

 minal mucus slit or pore. (See fig. 524, p. 2U2.) This 

 difference is considered of generic value by most authors,* 

 among others by Albers and v. Martens, whose descriptions 

 of genera we adopted in our work. They place, however, 

 in the genus Hyalina many species which are known to 

 possess the mucus slit (or some modification of it), as H. 

 olivetorum and H. nitida (see Moquin Tandon), and H. 

 fuliginosa, Imvigata, inornata, suppressa (see Terr. Moll. 

 U. S., ii). We have ourselves observed it in the following 

 additional species, H. cellaria, viridula, indentata, intertexta, 

 ligera, demissa, capsella, lasmodon and multidenta, and in 

 Zonites hopnodes, sculptilis and gulari.s. Its having been 

 overlooked l)y many European authors in so common a 

 species as cellaria-\ leads to the supposition that it really 

 exists also in other species now referred to Hyalina. We 

 propose, therefore, to place in the genus Zonites the species 

 in whicli the caudal mucus pore or slit has been actually 

 observed, restricting Hyalina to those without it. We have 

 not had an opportunity of examining all the species, but 

 have failed to discover any pore in Tennessee specimens, 



* But not by Messrs. Fisclier and Crosse in their magnificent work " iitudes sur les 

 MoUnsques Terrestres et Fluviatiles tlii Mexique et du Guatemala" (page 150), -where 

 Zonites and Hyalina are considered generically identical. 



t No mention of the caudal mucus gland in Z. cellarius is made in the monographs of 

 Draparnaud, Moquin-Tandou, Reeve, Forbes and Hanley, Gi-ay or Gwyn Jeffreys. 



