OF WESTERN SIND. 115 



marked with a very fine longitudinal striation. A few other spinelets, more delicate, 

 elongate, and subcylindrical, are also present ; these do not appear to be the shafts of 

 pedicellarise. 



Young Form. A smaller specimen than the type, from another locality, measuring 

 33 millim. in diameter, which we regard as belonging to the same species, presents 

 several interesting features worthy of note. The scrobicules are perfectly circular, 

 excepting the faintest trace of flattening in one or two instances at the ambitus ; and 

 the scrobicular ring is more nearly complete, being imperfect on the aboral margin of 

 the plate only. The miliaries that form the ring are distinctly larger than any of the 

 rest, and those in the miliary zone are quite microscopic and represented only by most 

 feebly developed and widely spaced granules. In the interporiferous (ambulacral) area 

 the granulation is also very minute. The outermost granule, although almost micro- 

 scopic, is the only one present throughout ; the second is only sometimes represented ; 

 and the occurrence of any trace whatever of the innermost miliary is most uncertain, 

 the space for its presence alone being always maintained. 



Remarks. It is not without considerable hesitation that we have placed this mag- 

 nificent form in the gepus Porocidaris, presenting as it does in such a very feeble manner 

 the primary character which would at first sight be regarded as the most conspicuous 

 feature of Desor's genus. The presence of the pits is not of such great importance, 

 however, after all, it being a character subject to extreme variation, and often absent 

 altogether in the existing species of Porocidaris*. After careful study of the fossils 

 under notice, we feel justified in adhering to the present determination. 



Dimensions. The largest specimen (which is rather distorted) measures about 

 48 millim. in breadth, and about 25 millim. in height. The smaller specimen is 

 33 millim. in breadth, and 17 millim. in height. 



Localities. In the Khirthar series of strata : — i. Twenty-four miles west of Kotri 

 (entering the hills on the road to Bula Khan's Thana). Survey-number ^^. 



ii. Uncertain, said to be from near Jakhmari, Laki range. Survey-number 



G304 

 21 • 



Illustrations of the Species in Plate XXI. 



Fig. 10. The test seen in profile: natural size. 



11. Actinal view of a part of the test: natural size. 



12. An interambulacral plate, with the adjacent portion of the ambulacral 



area: magnified. 



13. Ambulacral plates : magnified. 



14. Outline of fragment of a spine : slightly magnified. 



* Wyville Thomson, " On the Eehinoidea of the ' Porcupine ' Deep-sea Dredging-Expedition," Phil. 

 Trans, vol. clxiv. (1874), p. 727. 



