12 SECOND T ARK AND MISSION. 



26. VALVATA PISCINALIS, Mull. 



Nerita piscinalis, Miiller, Hist. Verm., p. 172. 



About thirty specimens from the Pankong Lake, quite undistinguishable from European 

 specimens. 



27. VALVATA STOLICZKANA, n. sp. Figs. 3436. 



This is a distinct and interesting new species ; in its size and depressed form it resembles 

 V. depressa, C. Pfr., Kiister, pi. xiv, figs. 20 & 21 ; it can be at once distinguished from it 

 by the remarkably deep and narrow umbilicus, only half as open as that of Pfeiffer's shell. 

 There are four whorls, which are slightly subangulate, forming a faint depression near the 

 suture ; under the lens it is distinctly, closely and regularly striated ; the colour is a light 

 glossy green, the aperture is not perfectly circular and is not quite so broad as high. 



Diam 4, axis If mm. 



Abundant at Yarkand. 



28. PISLDIUM, n. sp. 



It is a great pity that the figures in Clessin's new monograph of Pisidium, in Kiister's 

 edition of the " Conchylien- Cabinet," are so bad as to be almost without exception perfectly 

 unrecognizable ; a glance at Baudon's figures, " Monog. Pisidies Francaises," published in 1857, 

 will show the great inferiority of the former ; the shell described by Clessin as CorUcula (?) 

 minima io. "Fedsch. Moll., " pi. iii., fig. 30, is a most remarkable form, and I hope Dr. von 

 Martens will give us further and more correct information as to its proper classification. 



The present species bears a close resemblance to European forms of P. pulchellwm ; 

 it is certainly not allied even to the species represented in Fedschenko's Mollusca ; the 

 form is well characterized by its obtuse and tumid umbones, by its extreme shortness, 

 by its distinct concentric sculpture, and by its light- grey (cineraceous) colour ; it some- 

 what resembles Baudon's pi. i, fig. E (P. obtusale), but is less extremely tumid, and 

 not so high, compared with its breadth ; compared with pi. iii, fig. D, loc. cit., it is not 

 so high, more tumid at the umbones, which are less central, and Baudon's shell is 

 apparently smooth ; the position of the umbones is exactly represented by pi. ii, fig. H. 

 (P. limosum), loc. cit., from which indeed the Yarkand shell would seem to be scarcely 

 separable. 



Diam. 3, alt. 2^, crass. 2| mm. 



Abundant at Yarkand. 



29. PISIDIUM, n. sp. 



This is a very small, almost circular species, flatter than the last when of the 

 same size and with the umbones less tumid and more central ; the sculpture is the same : 

 it is more tumid and less polished than the next form, with the sides less produced and more 



