18 CHONDRIN.E OF THE ALPIC CENTER. 



mentary and almost concrescent with the second fold. Aper- 

 ture not rarely narrowed angularly at the base. South Tirol, 

 Salurn on the Litschbach, on limestone (Pupa avena Gredler, 

 Tirol, p. 104. Torquilla avenacea, var. gredleriana Clessin, 

 Moll.-fauna Oesterreich-Ungarn, p. 229). 



Var. riviana Schroder. PL 1, figs. 9, 10. Shell narrowly 

 umbilicate, fusiform-conic, finely striate or smooth, corneous- 

 brown to dark brown, often \vith a bluish wash ; 7-8 weakly 

 convex whorls; neck somewhat flattened, compressed into a 

 weak keel beneath; aperture large, ovate, obliquely truncate 

 above; throat with 8 folds: 2 each on the parietal wall (the 

 one next to the outer lip sometimes divided) and on the colu- 

 mella, 4 on the palate, the upper small, the next long and 

 reaching the margin, the last somewhat shorter; peristome 

 sharp, white, weakly lipped, somewhat reflected at the colu- 

 mellar margin. Alt. 7-10 1 /2> breadth 3-4 mm. (Schroeder). 



Austrian Tyrol : cliffs on the banks of Lake Garda, at Tor- 

 bole and Riva, especially on the numnaulitic limestone of Monte 

 Brione, usually in company with Chondrula quadridens and 

 Torquilla frumentum (Schroder). 



Modicella riviana SCHROEDER, Nachrbl. d. Malak. Ges., vol. 

 45, 1913, p. 173. 



It differs from Modicella avenacea by its size, the wide 

 mouth, the number and strength of the folds (avenacea 7, 

 riviana. 8) ; from M. megacheilos Jan by the more fusiform 

 shape, the sharp peristome which lacks a flattened lip, and the 

 number of teeth (megacheilos 9, riviana 8). The varieties in- 

 troduced by Clessin, megacheiloid'.es, transiens and gredleriana, 

 from other districts of the southern Tyrol, have nothing to do 

 with it (Schroeder). 



Cf. also Westerlund's notes on the same form. Malak. Bl.,, 

 xxii, p. 63, and Gredler, Nachrbl., 1885, p. 37, paragraph 3. 

 Specimens collected at Riva by J. L. and A. L. Baily (pi. 1, 

 figs. 9, 10) show considerable variation in shape and size. 

 Whether it is to be ranked as a species, or as a subspecies of 

 avenacea- or megacheilos is a question to be decided when the 

 intermediate forms abounding in the Tyrol shall be revised 

 with adequate material. 



