302 R. Biillen Neicton — Marine Fossils from Mekran Coast. 



above, tlien succeed five rounded ribs extremely close together with 

 very narrow interstices, these being succeeded by a series of five 

 or six more prominent and more widely sepai'ated ribs which are 

 nearly equidistant from each other. 



This species is represented by only one shell, showing external 

 dorsal characters. The vacant space on the body-whorl indicates 

 a considerable absence of shell structure, although the sculpture 

 details are well preserved in the neighbourhood of the aperture and 

 the base. It appears to differ from other species, both fossil and 

 recent, in the possession of a prominent postei'o-central rib and the 

 general irregularity of the rib system. 



The specific name of this shell is given as a slight acknowledge- 

 ment to Mr. F. W. Townsend for having collected and sent to 

 London so interesting a collection of specimens illustrative of the 

 geology of the Mekran coast. 



Examples. — One specimen only. 



DoLiuM cf. HocHSTETTERi, K. Martin. (PI. XVII, Figs. 2, 3.) 



DoUum Eochstetteri, K. Martin: "Die Tertiarscliicliten auf Java," 1879-80, p. 39, 

 pi. vii, fig. 8. 



It is interesting to find in this collection two examples of a DoUum 

 which show a greater regularity of sculpture details than was 

 observed in B. Townsendi. These possess a system of ribbing which 

 strongly resembles what is present in Martin's DoUum Eochstetteri 

 from the Upper Tertiaries of Java, and which approaches it also in 

 general contour. The chief difference is probably the occasional 

 presence in the Mekran specimens of an obscure median rib between 

 the more prominent ones, which are not observable in Martin's 

 figures. Among living shells this form of DoUum is related to 

 D. costutiim of Menke and Lamarck's D. maculatum, both well- 

 known Indian Ocean species. The smaller of the two shells consists 

 only of the body- whorl and the twisted anterior prolongation. The 

 dorsal diameter of the larger specimen is 35 mm. 



Examples. — Two specimens. 



EXPLANATION OF PLATES. 



Fi'^ures are dra\vn natural size, except a few magnifications which are introduced to 

 ° illustrate shell structures. 



PLATE XVI. 



Carbium Melvilli, n.sp. 

 Pig. 1. — Right valve, showing rib structure on ventral margin. 

 2. — Magnified view of ribs, as preserved on Fig. 1. 



" ^- \ Views of a smaller specimen of the same species. 

 „ 4. j 



Arca Blanfordi, n.sp. 



5_ Rio-ht valve, showing costa^ and striated internal surface at the fracture in 



" the ventral region : drawn from wax impression of specimen. 



Mactra mekranensis, n.sp. 



,, 6.— Right valve, with small patch of sculpture. 

 ,, 7. — Magnified view of sculpture. 



