150 Dr. J. W. Gregory — Egyptian Echinoidea. 



The echinids in the Egyptian Geological Survey Collection include 

 79 specimens, which are referred to 15 genera and to 30 species, of 

 which three are new. The horizons ai"e known in each case, but the 

 localities are not stated for one set, which apparently belong to an 

 old collection preserved in the Cairo Museum. 

 The horizons represented are as follows : — 



Pleistocene. 



Middle Miocene — Helvetian Series : Siuah. 



Upper Eocene — Bartonian Series. 



Middle Eocene — Mokattam Series. 



Lower Eocene — Libyan Series. 



Cretaceous — Turonian. 



Genus EHABDOCIDAETS, Desor, 1856. 



1. Ehabdocidakis Libtensis, n.sp. 

 Diagnosis. 



Test large and depressed ; width much greater than the height. 

 The shape is decagonal, with the sides all concave. The ambulacral 

 ai'eas occupy deep depressions, while the central suture of the inter- 

 ambulacral areas is also depressed. 



Inter ambulacra. — Each vertical series consists of nine or ten plates. 

 The tubercles are very prominent, the bases are perforated, and the 

 mamelons strongly crenulate. The scrobicular areas are not con- 

 fluent, but separated by one or two lines of granules. The 

 scrobicular circles are well developed, the granules being much 

 larger than those covering the rest of the plates. The tubercles 

 are separated from the ambulacral suture by a series of small 

 crowded granules, of which there are four or five rows at the 

 ambitus. The granulated area between the tubercles and the 

 median interambulacral suture is about twice as wide as on the other 

 side ; it is ornamented at the ambitus by six or seven rows of 

 granules. 



Ambulacral plates. — About eleven correspond to an ambital inter- 

 ambulacral plate. The pores of each pair are very wide apart, but 

 aie connected by a well-developed groove. The granular area down 

 the middle of the ambulacrum is wide, and consists of two large 

 and one or two small granules on each ambulacral plate. 



Apical area large, pentagonal. 



Dimensions. 



mm. 



Height of test 35 



Diameter of test ... ... ... ... ... ... 54 



Diameter of apical system 18 



Ambulacrum: width of poriferous zone at ambitus ... 2 



width of interporiferous zone at ambitus ... 4 



Interambulacrum : height of ambital plate 7 



width of ambital plate 13 



width of median granulated area of 



interambulacrum at ambitus ... 4 



Distribution. — Lower Eocene — Libyan Series : near Assiut ; 

 Coll. Geol. Surv. Egypt, No. 629. 



