234 ECHINODERMATA—ECHINOIDEA SUB-BRANCH III | 
— 
pyriform, situated between the peristome and posterior edge of the test. 
Apical system small, central. Jura and Cretaceous. 
Pileus, Desor. Test large, sub-hemispherical dorsally, flat actinally. 

FiG. 375. 
A, B, Holectypus orificatus, Schlot. Upper Jura; Streitberg, Franconia. C, D, H. depressus, Leske sp. 
Middle Jura; France. Apical system and ventral surface (after Cottean). 
Tubercles small, irregularly arranged. Periproct supra-marginal, small, 
broadly ovoid. Upper Jura. 
Pygaster, Ag. (Fig. 376). Test large, depressed dorsally, concave actinally. 
Amb straight, similar, flush or slightly raised, 
widest at the ambitus. Poriferous zones 
straight, simple, narrow ; tubercles of interpor- 
iferous areas in two or four vertical rows ; those 
of the /dmb in horizontal rows.  Peristome 
large, decagonal, with jaws and feeble perignathic 
girdle. Periproct immediately beyond the apical 
system. Jura and Cretaceous. 

SecTIoN I].—Perignathic girdle with well- 
developed interambulacral ridges ; ambulaeral pro- 
cesses rudimentary or absent. 
Discoidea, Klein (Fig. 377). Test hemi- 
spherical above the margin, flat actinally. dmb 
narrow, with some compound plates near the 
ambitus and actinally ; pairs of pores very 
numerous, small. J4mb with distinct median 
sutures, and small, perforate, and crenulate 
Fic. 376. Ome : 
apes ,.. . tubercles. Plates within the actinal surface 
Pygaster umbrella, Ag. Oxfordian ; A Tee i é . 
Chatillon-sur-Seine. Young individual, with radiating ribs, ten in all, extending as far 
after Cottean). B 5 
= d as the peristome; appearing on casts as deep 
depressions. Periproct small, inframarginal. Cretaceous. 

Se 

Fic. 877. 
Discoidea cylindrica, Ag. Upper Cretaceous; Liineburg. A, Side-view. B, Test broken open to show the 
inner partitions, 1/,. 
Conoclypeus, Ag. (Fig. 378). Test large, thick ; conical or vaulted dorsally, 
