218 Frof. J. W. Gregorij — FoshU Echinoidea 



beach deposits of WacH Feiran may be a fragment of a Miocene 

 species. The only species from that locality which is satisfactorily 

 determinable is an Echinolampas, which is a Lower Cainozoic or 

 Miocene species. Hence it may be that the three species of Echinoids 

 from the beach deposits of Wadi Feiran are remanie from a Miocene 

 or Lower Cainozoic horizon. 



I must express my best thanks to Captain Lyons for having 

 allowed me to keep the collection so long, in spite ot the unavoidable 

 delays in the preparation of a report upon it. 



I. CRETACEOUS. 



Subclass REGULARFA ECTOBRANCHFATA. 



Suborder DFADEMINA. 



Family DIADEMATID^. 



HETERODIADEMA, Cotteau, 1864. 

 Heterodiadema bigranulatum/ n.sp. (PI. X, Figs, la-/.) 



Hiagnosis. — Test small, low; well flattened above and below; 

 the ambitus is tumid. 



Apical area large, its length is half the diameter of the test ; and 

 the ratio of breadth to length is 7 to 9 (it is 21 : 29 in H. lihycum). 

 In shape it is nearly pentagonal ; the three anterior sides are 

 straight, while the two posterior sides are somewhat convex. 

 Peristome small. 



Ambulacra, 13-14 compound plates in each vertical series; the 

 passage from the large tubercles on the ambitus, to the smaller ones 

 near the apex, is less sudden than in H. libycnm. 



Interambulacra, 10 compound plates in each vertical series; the 

 scrobicular areas are not confluent, but occasionally the scrobicular 

 circles become very thin, and the granules somewhat scanty ; there 

 are two granules in each of the horizontal rows (instead of the four 

 in H. lihycmn) between the base of the boss and the median suture. 



Dimensions : 



Diameter 



21 mm. 

 8'5 mm. 

 9 „ 



5-5 „ 



Height 



Width of apical area 



Length of apical area 



"Width of ambulacrum at ambitus 



Width of iuterambulacrum at ambitus ... ... S ,, 



Bistrihntion. — Cenomanian : southern slope of Jebel Gunneh, 

 Sinai. L 350G. Collected by Dr. W. F. Hume, 1899. 



Figures. — Pi. X, Fig. 1«, from above, nat. size; Fig. 1&, from the 

 side, nat. size; Fig. \c, a compound ambulacral plate showing the 

 granulation, by 4 diam. ; Fig. Id, a worn ambulacral plate showing 

 the sutures, by 4 diam. ; Fig. \e, iuterambulacral plates showing 



^ From its double rows of granules around the bases of the ambital interambulacral 

 tubercles. 



