GENERA AND GROUPS OF THE ECHIKOIDEA. 83 



Gypliosoma Heinzi thus becomes Peronia Heinzi, Peron et 

 Gauthier, sp. 



Grenus Echinopsis, Agassiz, 1810, Gated. Syst. Ectyp. Ech. p. 18. 

 Be.sor, 1854, Synopsis, -p. 98 (pars). De Loriol, 1881, Eoc. 

 EcJi. aus ^gypt. u. d. Lib. TVuste, PalceontograpMca, n. F. 

 X. i. (xxx.) p. 10. 



Test tliin, small or moderate in size, hemispherical, or sub- 

 conical and tumid abactiuallj, rather flat actinally. 



Apical system uarrow, the basals uuequal ; the radials small 

 aud close to the periproct, but not forming its ring. Periproct 

 large. 



Ambulacra large, straight, flush with the test ; pairs o£ pores 

 in simple straight series ; plates compound, triple, or quadruple, 

 made up of low broad primaries; tubercles very small, close, 

 perforate and uon-creuulate, extending the whole length of the 

 ambulacrum in two vertical rows placed near to the poriferous 

 zones. 



Interradia with two vertical rows of small primary tubercles, 

 slightly larger than, but otherwise similar to, those of the ambu- 

 lacra ; minute granules surrounding the non-sunken scrobicules. 

 Sutures of the plates distinctly seen. 



Peristome small, slightly depressed ; branchial incisions slight. 



Fossil. Eocene : Europe, Egypc. 



EcMnopsis Edwardsi, Eorbes, of the London Clay, is an 

 Echinopedina. 



Genus Gymnodiadema, De Loriol, 1884, Eecueil Zool. Sioisse, 

 vol. i. No. 4, p. 606. 



Test tliin, tall, swollen, moderate. 



Apical system flush ; the madreporite triangular, slightly deve- 

 loped ; radial plates small. 



Ambulacra narrow ; poriferous zones straight, with regularly 

 superimposed pairs of pores in simple series ; the plates very 

 numerous, low, narrow primaries ; interporiferous areas very 

 narrow, have abactinally very small granules, which are barely 

 visible to the naked eye, yet forming vertical series ; they are 

 replaced actinally by very small tubercles with perforate 

 mamelons. 



Interradia very broad, covered with granules like shagreen ; 



6* 



