PELEOYPODA. 51 



The internal cast of the lower valve is generally short, its length seldom 

 exceeding 40 mm., diameter at the upper end is not more than 30 mm., and at the 

 lower end the diameter is ahout half of that of the upper end. The cast is there- 

 fore short and conical, its lower end being more or less straightly cut off, hut always 

 somewhat rounded. The lower valve must have spread out into rather a broad 

 foliaceous rim at its upper end, as some specimens distinctly show. Two rather 

 long but narrow dental grooves are always well marked. Surface smooth, but 

 extremely finely striated in a longitudinal direction. 



Loeality and straiigraphioal position, — D6s valley. 



Remarks. — The species described above is one of the commonest forms in 

 the Des valley, where there occurs a special bed entirely filled with the curious 

 conical casts of the lower valve. To judge from Romanowski's figure 4 a, the forms 

 which have been found in Baluchistd,n must be identical with the species which 

 he describes under the name of Sphcerulites dilatata, but being unable to read 

 the description of this species in the Russian language, I cannot say how far my 

 supposition is correct. But it seems to me that he has described under the name of 

 Sphcerulites dilatata two species which are apparently different. Eig. 4 a repre- 

 sents a slightly tapered, nearly cylindrical cast, cut off straight at the lower end, 

 vrhile fig. 4 b represents a short, conical cast, with a pointed end. In Turkestan 

 these two extreme shapes may have been connected by intermediate links, but in 

 Baluchistan the two types are certainly different, not only as regards their shape, 

 but also as regards the ornamentation of the surface. I have therefore separated 

 them, and I shall describe the conical cast under the name of Sphcerulites 

 muschketoffi. 



Stoliczka has described as Sphcerulites mutabilis a form from Southern India, 

 the internal cast of which resembles Sphcerulites dilatata to some extent, but the 

 ornamentation of the surface of the shell is entirely different in the two species. 



Rabiolites MUSCHKETOFPi, spec. nov. PI. XIII. fig. 1, 2-2A, 3-3a. 



Like the former species, this form is only represented by internal casts of the 

 lower valve. These do not exceed 45 mm. in length, having a diameter of about 

 30 mm. at the upper end. They are conical in shape, and resemble a short, truncated 

 slightly curved horn. Two rather long dental grooves are always well marked. 



The ornamentation consists of numerous rather coarse longitudinal striae, 

 which are rendered somewhat irregular by concentric strise of growth. 



Nearly all the specimens prove that the lower valve expanded in a broad, 

 probably somewhat foliaceous rim at the upper end, which was well marked off by 

 a sharp line from the lower conical part of the shell. 



Locality and stratigraphioal position — Dds valley. 



Bemarks.— This species is as common as the former in the Des valley, but, as I 

 have already remarked, it is easily distinguished from it by the attenuated conical 

 shape of the internal mould of the lower valve. Fragments of the surface of the 

 shell have proved that in Radiolites muschketoffi the ornamentation consisted of 

 much coarser longitudinal striae than in BadioUtes subdilatata. 



H 2 



