OF WESTERN SIND. 187 



Fig. 4. Actinal view of another test : natural size. 



5. The peristome and surrounding portions : magnified, 



6. Abactinal view of an abnormal specimen, in which the odd anterior 



ambulacrum is aborted : natural size. 



2. Rhtnchopygus pygm^us, Duncan ^ Sladen. Plate XXXIII, Figs. 7-16. 



Ehynehopygus pygmsBus, Duncan Sf Sladen, Pal. Ind., Poss. Echin. Western Sind, Fasc. ii. (Eanikot 

 8eries), p. 61, pi. xv, figs. 5 & 6. 



It was remarked in the preceding fasciculus of this work, when describing the 

 Echinoidea of the Eanikot series, that the present species differs from B. Calderi mainly 

 in its small size and in the different shape of the test, the disproportion of length to 

 breadth being less, the abactinal area being regularly convex, without any trace of the 

 longitudinal keel, and the posterior truncation barely existing. Furthermore, the peri- 

 stome is more regularly pentagonal, and the bourrelets are more sharply tubercular than 

 in R. Calderi. Excepting these points, the general details of the characters of these 

 small tests accord very closely with the description of R. Calderi ; and under these cir- 

 cumstances we deem it unnecessary to add to our previous remarks. When studying 

 the few Eanikot specimens of this species we were inclined to think that the form under 

 notice might perhaps prove to be only the young of a variety of i?. Calderi, or even of 

 i?. Calderi itself. With the larger series of examples from the Khirthar beds now at 

 our disposal, we consider that such a supposition is almost untenable. The form has 

 been collected at a number of stations ; and although a considerable amount of variation 

 is found when the series from different localities are compared, and even amongst indi- 

 viduals from the same locality, we are unable to detect a transition between i?. fygmosus 

 and H. Calderi. Young specimens of i?. Calderi, of equal size to the present species, 

 present all the characters of the adult form ; whilst, on the other hand, examples which 

 appear to be abnormally large ioxB.pygmoeus maintain the characters and general facies 

 above defined. 



BemarJcs. The chief variations occurring in this inconstant form are those which 

 affect the relative proportions of length, breadth, and height, together with the position 

 of greatest breadth. A remarkably depressed example occurs, bearing the Survey-number 

 ^^, in which the abactinal area is very low, the margins tumid, the contour prominent 

 anteriorly and truncate posteriorly, and with the periproct wide and exposed. This 

 latter character appears to be owing to damage of the test through weather-wearing. 

 Had this abnormal form been represented only by a solitary example, it would have 

 probably been placed as a well-marked variety. From the fact, however, that other 

 depressed specimens occur from Stations 117 and 112, which appear to us to form a 

 transition with the normal type of the species, any nominal recognition of the variation 

 would seem undesirable. The specimen is drawn in Figs. 15 & 16. 



A large and very elongate example comes from Station 111 c, which in marginal 

 contour resembles the contour of B. Calderi when seen from below more nearly than 

 any other specimens we have examined. The abactinal surface is low even for B. 



