ECHINOIDEA. 13 



ranged in slightly oblique pairs ; near tlie ambitus three pairs of pores are formed into 

 obliquely placed groups; this arrangement disappears, however, towards the apex 

 and mouth. Tubercles small, the mamillary eminence small and perforated, the boss 

 comparatively large aad not crenulated, the scrobicule narrow but deep, sur- 

 rounded by a complete circle of secondary tubercles. 



On the ambulacral area there are two very regular rows of tubercles, of which 

 about one comes on every three ambulacral plates. There are about 30 tubercles in 

 each row, which decrease in size from the equator to either pole ; in the miliary zone 

 there are two rows of secondary tubercles, between which there are some small gra- 

 nulations. On the interambulacral area there are twp rows of primary tuber- 

 cles, slightly larger than those of the ambulacral area, which extend from the 

 apex to the mouth ; on either side of each of these rows there are two rows of 

 secondary tubercles, which do not reach up to the apex, but probably extend to 

 the mouth ; the two lines next to the primary row reach rather high up on the upper 

 surface, but disappear before they reach the apex. As regards the relative size of 

 the tubercles, those that compose the outer rows are a little smaller than those of the 

 inner ones ; fine granules are sparsely and irregularly distributed between the 

 primary tubercles. Peristome unknown. 



Locality and stratigraphical position. — Des Valley, horizon 4. 



Bemarks. — The specimen above described is considerably damaged, but those 

 parts which remain, exhibit the features sufficiently well to allow of its determina- 

 tion. The chief difficulty arises from the weathered state of the test, as it is not 

 easy to decide whether the tubercles are perforated or not ; a few tubercles, however, 

 show minute holes, so that although no traces are left on the majority of them, 

 it is quite certain that the tubercles were perforated and not crenulated. 



Cotteau states^ that the genus Orthopsis forms part of the Diadematidse, with 

 perforated non-crenulated tubercles. Its chief features are the numerous small tu- 

 bercles on the ambulacral and interambulacral areas and the regular straight am- 

 bulacral plates separated by conspicuous sutures, features which are well noticeable 

 with the above specimen, so that there is no doubt as to its generic identity. 



The nearest relation of Orthopsis perlata is Orthopsis ovata, Cott., which has, 

 however, only 8 rows of tubercles on the interambulacral areas instead of the 10 of 

 the Baluchistdn species. Orthopsis granularis, Cott., and Orthopsis miliaris, Cott., 

 sp., are distinguished by the still smaller number of rows of tubercles on the in- 

 terambulacral areas and by their generally smaller size. 



Genus : CYPHOSOMA, Agassiz. 



Ctphosoma sp. 



The only specimen by which this genus is represented is a small, much worn, 

 and deformed test of 22 mm. in diameter, circular in shape, with a depressed upper 

 surface and a slightly pulvinated lower surface; apical disc destroyed, ambulacral 



' PaMpntolpgie franfaise ; Terr, cret., Eohinodermes, Vol, VII, p. 551. 



