'-' I PROCEEDINGS OF 'I'm: MALACOLOGICAL SOCIETY. 



METOSTEACON, A NEW SLUG -LIKE GENUS OF DAET-BEARING 



EEL It'll). E. 



l!\ II 1 m;\ A. PlLSBRY. 



Read 10/// November, 18'J'J.. 



PLATE 111. 



Recent studies on American Land-snails show that the helicine group 

 Bologona Euadenia ' is richer in genera and more widely vaiied in 

 structure than could have been suspected at the lime il was Hounded 

 in IS 1 .),".. 



In the genus Metostracon, now to he described, we at Length have 

 a slug dorived from the true ' Helix* stock; and while the external 

 form is remoulded to conform to the slug-like appearance, and the 

 shell is uncoiled and completely buried, yet the soft parts unmis- 

 takably indicate its helicine antecedents. 



It might be thought that a genus of slugs in the ETelicidue is no 

 novelty, for Fischer 8 places several slug-like genera in that family. 

 When, however, we subtract from Fischer's heterogeneous group the 

 genera of Aulacopod Pulmonates (Endodonticke, Arionidce, etc.), which, 

 of course, have nothing to do with the Helices, we find nol a single 

 slug- like genus remains. 



With the new genus Metostracon, it is proposed to associate the less 



modified Xanthonyx, 3 which has been anatomically examined by Strebel 

 and Pfoffer( A'. Cordovanus), and by myself ( A'. Salleanus). Since there* 

 is no known genus bearing so close a relationship to Metostracon as 

 XanthonyJC, 1 shall here describe the latter by way of comparison 

 w ith my new genus. 4 



Anatomy ok Metostracon. 



External Features (PL III, Fig. 1). — Slug, with the submedian 



mantle somewhat elevated, or humped, the general form like 

 Hemphilh'a, but less elevated; sole undivided; lateral edges of foot 

 without trace of pedal grooves or fo.it margin; no distinct furrows 

 on the median line of back or tail, and no genital groove ; tail not 

 keeled above, simply pointed behind; reticulation of the surface 



1 •• Ghiide to the Study ct' Eelices" : Manual of Conchology, ser. n, vol. i\, p. 175. 



- Manuel de Conchyl., pp. 461 IT:!. Fischer's Helicidaa include representatives of 

 no less than seven well -characterized families, as follows: Ajionidse, with the 

 genera drion, Ariolimax, etc.; Endodontic!©, with Patula, Endodonta, etc.; 

 Zouitidce, T . Pseudohyalina; Erocoptidse, Berendtia; Achatinidse, 



Rhodes; Bulimulida), ' JPachyotis ' ; and Helicidte, Helix, etc. 



3 I formerly considered Xanth »yx to be a synonym of Binneya: cf. Pilshry & 

 Vunatta, b'roc. Acad. .Nat. Sci. Philad., LS9S, p. 229. This view was completely 

 eiToneous. 



i In explanation of certain points left in uncertainty or ignored in the following 

 accouut, it should be said that 1 have hut two specimens of Metostracon, one 

 o\ which it was thought best to preserve uncut, and only a single example of 

 Xanthonyx. 



