178 PEOP. p. M. DTTlSrCAlSr's EBVISION OF THE 



and more or less truncated, low and arched dorsally, flat or con- 

 cave actiually ; grooved or not posteriorly. 



Apical system excentric in front, small, and with four per- 

 forated basal plates. 



Ambulacra flush, unequal, long, open, and subpetaloid, the 

 pores unequal ; zones broad. 



Peristome sunken, excentric in front, oblique, subpentagonal, 

 with only slight doubling of pairs of pores, and no true floscelle. 

 Periproct supramarginal, oval, elongate. Tubercles nearly equal 

 in size throughout. 



Fossil. Cretaceous : Europe, Asia (S. Hindustan), N. Africa. 



G-enus Ilaeiona, Barnes, 1877, PalrBontographica, n. F. i. (xxv.) 

 p. 34. 



Test elongately oval or oviform, subdepressed, more or less 

 convex above, flat or slightly convex below ; margins very thick 

 or tumid. 



Apical system compact, excentric in front. 



Ambulacra petaloid ; petals short, unequal, lancet-shaped, 

 contracting and nearly closed. Poriferous zones equal ; pores 

 round or oval, conjugate. 



Peristome decagonal or subdecagonal, with a raised rim and 

 special tubercles. Eloscelle absent. Periproct elongately oval, 

 on the upper part of the posterior vertical truncation of the 

 test. 



Ornamentation very uniform ; tubercles small, sunken in deep 

 scrobicules, close ; miliary granulation confluent and compact. 

 A more or less bare band between the peristome and periproct. 



Fossil. Eocene: Europe, Asia (Sind). 



The peculiar and distinctive structure of the peristome was 

 discovered and carefully pointed out by "W. Dames. He notices 

 (Ech. d. Yicent. u. Yeron. Tertiar. p. 34, Palseontographica nt 

 supra) the outline is decagonal, which might be represented by 

 an equilateral pentagon from which the angles had been abruptly 

 truncated by short lines — the long lines, corresponding with the 

 interradia, being granular, whilst the short lines, corresponding 

 with the ambulacra, are smooth. At the junction of the long 

 and short lines a small smooth tubercle is present, the peristome 

 being therefore surrounded by ten of these protuberances. 

 The margin of the aperture is raised, and extends far into the 

 body-cavity. 



