ECHINOIDEA. 31 



alrger tubercles, btit on the base they are sometimes arranged in scrobicular circles. 

 The course of the basal portions of the postero-lateral ambulacra divides the base 

 into a central and a lateral region, which show a marked difference in the size of the 

 tubercles ; on the plastron they are not only generally smaller than on the lateral 

 region, but they also decrease in size from the edges towards the centre of the broad 

 band which extends from the mouth to the posterior border. The lateral region 

 forms a moderately broad band along the circumference, and the tubercles decrease 

 in size from the inner edge tovfards the periphery ; it must be particularly noted 

 that they do not extend above the ambitus. Between these two regions only very 

 minute granules occur, which easily wear off ; a few tubercles of larger size are also 

 seen around the periproct. 



Locality cmd stratigraphical position. — Upper cretaceous strata of the Pyrenees 

 very common in the Des Valley ; horizon No. 2, Des Valley ; horizon No, 4, 

 Maz^r Drik, horizon No. 8, (rare). 



Bemarks. — Although it may seem hazardous to consider a species occurring in 

 the cretaceous strata of Baluchistan identical with one which is found in the 

 Pyrenees, I think that my views will stand even the most rigorous examination. 

 The most striking coincidence will be found as regards the shape of the test. 

 Hebert gives the following proportional figures of H. pyrenmcus : — 



i = -84 -81 -84 



L 



r = -61 -638 -634 



Now, if these figures are compared with the ratios as given for the Baluchistan 

 form, it must be admitted that they are nearly exactly the same, and I have no doubt 

 that every one will agree with me that differences of "07 may be considered as 

 immaterial. 



Now, if we compare the profile of the two forms, we notice exactly the same 

 curve of the upper surface : nearly flat in the middle, dropping vertically on the 

 anterior sides, while it slopes just perceptibly posteriorly ; the lower surface is 

 convex, while the sides are nearly perpendicularly inclined ; the test has therefore 

 a barrel shape which forms the most characteristic feature of this species. 



The only differences which I can discover exist with regard to the distribution 

 of the larger tubercles on the lower surface, and the position of the anal opening. 

 If Hubert's figure is absolutely correct, the larger tubercles cover also the posterior 

 part of the smooth bands which represent the basal portion of the postero-lateral 

 ambulacra; on the other hand, the difference of size in the tubercles of the 

 plastron are distinctly visible in Hubert's figure, although it is obvious that the 

 tubercles are somewhat diagrammatical. 



As regards the position of the anal opening, it seems a little higher above the 

 posterior border in Hubert's fig. 4, than it is in the Baluchistan specimens. I am, 



