GASTROPODA. 65 



the same ; and although d'Archiac does not mention the spiral furrows on the 

 anterior half of the last whorl, they are distinctly marked on his figures 2a and 3. 



Stoliczka has already drawn attention to the fact that Nerita divaricafa, d'Orb., 

 in its type from Southern India, is probably identical with Otostoma ponticum. Now 

 I have before me Stoliczka's originals, and on comparing them with the specimens 

 from Baluchistan, particularly the original of pi. XXIII, figs. 11, 12, I cannot 

 discover the slightest difference. The form from Southern India exhibits all the 

 features of the ornamentation which have been described above as characteristic of 

 Nerita pontica. Since the Baluchistdn specimens agree so well with Otostoma 

 ponticum d'Arch., I think I am justified in considering Stoliczka's Nerita 

 divaricata as identical with that form. 



This species must have had a world wide distribution, as it ranges from the 

 Pyrenees through Asia Minor, Baluchistdn and as far as Southern India. 



Nerita d'akchiaci, spec. nov. PI. XIV. fig. 5-5b, 6-6a, 7-7A. 



This is one of the most common forms in the upper cretaceous strata of 

 Baluchistdn; in the D^s valley it apparently occurs in thousands. 



The shell, whose transverse diameter reaches 37 to 40 mm., is subglobose and 

 consists of three inflated whorls which rapidly increase in size. The spire is only 

 slightly prominent, but not so much depressed as in Nerita pontica ; the Isst whorl 

 is inflated and just a little concave near the suture. The ornamentation consists ■ 

 of exceedingly fine, regular, and very closely set longitudinal striEe, apparently re- 

 presenting strise of growth ; and if the surface of the shell is worn, stronger and 

 finer striae alternate very regularly. 



Aperture not seen ; outer lip sharp ; inner lip not observed. 



Locality and stratigrapUcal position. — Very common in the D^s valley, horizon 

 4 ; rather rare at Mazdr Drik. 



Bemarhs.—Tsyis, species is easily distinguishable from Nerita pontica by 

 its higher spire, but particularly by the seemingly smooth, finely striated surface 

 of the shell, a character by which it is also distinguished from other species belong- 

 ing to this genus. 



The composite character of the shell which Stoliczka mentions is exceed- 

 ingly well seen in this species. The outer layer is a black, apparently homogeneous 

 substance, which shows a conchoidal fracture. The inner layer is crystalline and 

 looks as if it were composed of an aggregate of crystals of calcite. The latter, 

 which forms the callosity of the inner lip, is in all the specimens more or less dissolved 

 and replaced by a rocky matrix which adheres so firmly to it that it is impossible 

 to lay the inner lip free. But there is not the slightest doubt, that a large 

 flattened inner lip existed, and that the aperture was rather narrow. If the matrix 

 which covers the inner lip is removed as far as can be done, it may be seen that the 

 crystalline layer below it extends to a considerable distance inside, narrowing the 

 aperture; but ordinarily no trace of this callosity can be seen. 



