from Sinai and Egypt. 219 



the ornamentation, by 4 diam. ; Fig. 2, JECeterodiadema lihycum 

 (Desor), two interambulacral plates, after Cotteau. 



Affinities. — This echinoid is a typical Heterodiadema ; it differs- 

 from IT. lihycum (Desor)/ the well-known type-species, by its non- 

 confluent scrobicular areas, and by having only two instead of 

 four granules in each row on the interambulacral plates. 



Family DIPLOPODIIDiE. 

 ACANTHECHmOPSIS,2 n.gen. 



Diagnosis. — Diplopodiidse with the ambulacra diplopodous abacti- 

 nally, whei'e the plates are long, thin, simple primaries; but with 

 uniserial epipodia on the actinal surface and near the mouth. The 

 ambital plates are of five primaries, one of which may be reduced 

 to a demiplate. 



There is a bare depression in the median line of the abactinal 

 part of the interambulacra. 



Tubercles crenulate and perforate. 



Type Species. — A. hiimei, n.sp. 



Distribution. — Cretaceous : Sinai and Southern Tunis. 



Affinities. — This species is most nearly allied to AcantJiechimis, but 

 it differs therefrom by its perforate tubercles. 



AoANTHECHiNOPSis HTJMEi, n.sp. (PI. X, Figs. 3a-e.) 



Test of medium size ; subpentagonal ; flat below, somewhat 

 turban-shaped when seen from the side. 



Ambulacra broad above, where the epipodia occur in long narrow 

 primaries. The ambital plates have five primaries, one of which may 

 be reduced to a demiplate, by being just crushed out from the 

 middle line. 



Intei'ambulacra, about 16 plates in a vertical series. The tubercles 

 begin as a single series, separated fi-om the series on the opposite 

 side of the interambulacrum by a bare depressed area. On the 

 seventh plate from the top a second line of tubercles begins, and 

 the ambital plates have three rows of tubercles in a somewhat 

 oblique series. 



Dimensions : 



Diameter 36 mm. 



Height .. ... ... 15 mm. 



Diameter of peristome 12*5 mm. 



Distribution. — Cenomanian : southern slope of Jebel Gunneh, 

 Sinai. L 3506. Collected by Dr. W. F. Hume. 



Figures. — PI. X, Figs. 3a and 6, test from above and from the 

 side, nat. size ; Fig. 3c, ambulacral plates near the apex, by 4 diam. ; 

 Fig. 3d, ambital ambulacral plates, by 4 diam. ; Fig. 3e, ambital 

 interambulacral plates, by 4 diam. 



' Pseudodiadema Ubycum, Desor, 1858: Sjti. E'ch. foss., p. 72. Heterodiadema 

 lihjcum, Cotteau, 1864 : Pal. fraiiQ., Terr, eret., vol. vii, p. 522, pi. 1124» 

 Cotteau, Peron, & Gautliier, 1879: E'ch. foss. Alger., fasc. 5, p. 201, pi. xv, fig. 5.. 

 Gauthier, 1889 : E'ch. foss. S. Hauts-Plat. Tunisie, p. 68. 



2 Like Acanthechinus. 



