226 HELICID^. 



quite a different shell, even if we omit mention of the most 

 conspicuous feature of fresh specimens, the membranous ribs, 

 which this species has in common with a number of other forms 

 of this group and the next [group of F. cyclophovella]. Between 

 each pair of these ribs are 3 to 6 fiuer strife ; and under the 

 microscope very fine lines are seen, nearly parallel to the lines of 

 growth at the suture, while on the periphery they are variously 

 intercrossing. The nucleus, or embryoual whorls, bear a number 

 of microscopic revolving lines, in this as well as in the other species 

 of this group. 



" F. costata is rather variable. The largest measure 2*7, the 

 smallest 2'1 mm. greater diameter. Always the sutural part of 

 the last whorl descends more to tlie aperture tlian the back or 

 peripheral part of the whorl, and sometimes the latter keeps 

 exactly in the horizontal direction to the very margin of the lip. 

 The number of ribs was found to be from 23-35 in the type. 

 Some forms differ so much that they are to be considered varieties." 

 {Sterki.) 



197. Vallonia ladakensis, Nevill. 



Helix ( Vallonia) ladacensis, Nevill, Scient. Results Second Yarkaud 



Mission, Mollusca, 1878, p. 4 ; von Martens, M^m. Acad. Imp. 



Sci. St. Petersburg, ser. 7, xxx, no. 11, 1882, p. 3, pi. 3, fig. 3. 

 Helix ( Vallonia) pulchella, var. ladakensis, Nevill, Hand List, i, 



1878, p. 75. 

 Vallonia ladacensis, Sterki, Man. Conch, ser. 2, viii, 1893, p. 260, 



pi. 56, figs. 19-21; Mollendorf=f, Ann. Mus. Zool. Acad. Imp. 



Sci. St. Petersburg, iv, 1899, p. 142. 



Original description : — " I have long separated this form, which 

 can be distinguished from all the varieties of H. costata at a glance 

 by its much more open umbilicus, at least half as open again ; it 

 is a much larger shell than typical H. costata, about the same size 

 (a trifle larger) as the above described var. asiatica ; the sculpture 

 is finer, closer together, and more beautifully regular ; the spire 

 is flatter, the suture more excavated ; the base is scarcely, if at 

 all, subangulate near the umbilicus, as it is in so marked a way in 

 the preceding ; one of the best characteristics of H. ladacensis is 

 the considerably higher and more expanded aperture with a cor- 

 responding less oblique columella ; the umbilicus is so much more 

 open that the whorls within can be clearly traced up to the apex 

 itself." (Nevill.) 



Diam. 3^, alt. Ik mm. 



Hab. India : Kashmir, Mataian, Dras Valley, Ladak (StoUczlri), 

 Leh, Ladak (StoliczJca) ; Spiti, Punjab {Stoliczka). W. Tibet 

 (Sioliczka), Turkestan : Tian-shan Mountains {Potanin). 



