PELBCYPODA. 43 



Stoliczka was of the opinion that regardless of the number of intermediate ribs 

 all the forms occurring in Southern India should be considered as one and the same 

 species, for which he adopts the name Vola qmnqueonslata. Inasmuch as the 

 forms with three intermediate ribs have never been found in any lower horizon than 

 the Ariyalur series, I do not see why the specific name of quadricostata should not 

 be retained for these forms. It would certainly not be advisable to call the Baluch- 

 istdn forms by the specific name quinquecostata, when they exhibit, without ex- 

 ception, three instead of four intermediate ribs. 



Locality and stratigraphical position. — Mazdr Drik, horizon 8. 



Genus : PECTBN, Klein. 

 Pectmn (Chlamys) dujardini, Roemer. PI. XII. fig. 1-lA. 



1841. Pectea diijardini, A. Boemer, Norddeutsch. Ereidegeb., p. 53. 



1843. Pecten dujardini, i'Orhigny, Pal. franc. Ter. cret., Vol. Ill, p. 615, pi. 439, figs. 5 — 11. 



The only specimen which I refer to this species is unfortunately too badly pre- 

 served to permit of a description of the general shape of the shell ; all I am able to 

 say is, that both valves exhibit the same ornamentation, and probably differed very 

 little as regards their convexity. The ornamentation consists of 8 broad rounded 

 radiating ribs, separated by interstices of the same breadth. Besides the principal 

 ribs there are much finer filiform ribs equally distributed over the whole surface ; 

 there were originally three on each main rib and one in the interstice, but tbe 

 number gradually increases to 5 on the ribs and 3 in the interstices. Ribs and 

 interstices are crossed by numerous, very regular lamellar striae of growth, some 

 of which when passing over the secondary ribs, are generally raised into low sharp 

 scales, following each other at regular intervals. 



Locality and stratigraphical position. — D^s valley, horizon 2. 

 Eemarks. — It is impossible to discover any difference, as regards the finer orna- 

 mentation of the valves, between the Baluchistdn form and the well known Pecten 

 dujardini : the only difference which I can discover is the larger size and an 

 apparently different number of larger ribs, of which the Baluchi8td,n form exhibits 

 onlv 8, while there are 11 in the European type. But as the specimen is 

 very much damaged, it is difficult to say whether it did originally exhibit 11 ribs or 

 not. One valve most distinctly shows 9 ribs, and it is quite possible that if the other 

 valve were completely preserved, it would also show the same number. However, I 

 do not think that too much weight should be put on this deviation, as, according to 

 GeinitzS the number of the main ribs varies from 9 to 11. Should, however, better 

 preserved specimens prove that the smaller number of ribs is a constant feature in the 

 Baluchistan type, the latter might as well be distinguished as var. Baluchistdnensis 

 from the European type. 



' Elbibalgebirge. Palaeontographica, Vol. XX, 2, p. 36. 



