226 ECHINODERMATA—ECHINOIDEA SUB-BRANCH III 
small tubercles, placed near the borders of the poriferous zone. LAmb primary 

Fig. 362. 
Tetraciduris Reynesi, Cotteau. Neocomian; Vergans, near Castellane, Basses Alpes. A, Test reduced one 
half. L, Portion of Amb, enlarged (after Cotteau). 
tubercles very large, crenulate, and perforate. Spines narrow, elongate. 
Lower Cretaceous (Barrémien) ; Europe. 
Order 2. DIADEMATOIDA. Duncan. 
“ Huechinoidea with an actinal, central peristome, and an abactinal periproct 
situated within the dorso-central system; with perfect or rudimentary or absent 
internal branchiae, with external branchiae and incisions in the peristome ; with jaws 
and teeth and a continuous perignathic girdle ; ambulacral plates alone continued 
beyond the peristome or as separate buccal plates. Spheridia present.’—Dunean. 
Sub-Order A. STREPTOSOMATA. Duncan. 
Test more or less fleaible, with eaternal and internal branchiae. Ambulacral 
plates alone continued beyond the peristome to the stoma. 
Family 1. EHchinothuridae. Wyville Thomson. 
Test thin, flexible. Coronal plates with imbricating membraneous edges. External 
branchiae small, internal sometimes very large. Tubercles small; spines short, 
cylindrical. 
This family is represented by two living and two extinct genera, the latter 
being known only by fragmentary specimens. Pelanechinus, Keeping, is found 
in the Upper Jura, and Hechinothuria, Woodward, in the Upper Cretaceous of 
England. Phormosoma, Wyv. Thomson, and Asthenosoma, Grube (Calveria, 
Wyv. Thomson), inhabit depths greater than 100 fathoms. 
Sub-Order B. STEREOSOMATA. Duncan. 
Test rigid, with eaternal branchiae and rudimentary or absent internal branchiae ; 
with isolated buccal ambulacral plates. 
