ORDER II 



EUECHINOIDEA DIADEMATOIDA 



227 



Family 1. Saleniidae. Desor (emend. Duncan and Sladen). 



Apical system large, with a persistent dwso-central plate or plates, which crowd 

 the anal orifice somewhat out of the centre of the periproct. Ambulacra narrow, with 

 a n merous, simple, low primaries ; rarely compound actinally. Interambulacral plates 

 few, with large tubercles. Teeth keeled. Spheridia present. Jura to Recent. 



The pivsenrr ,,f on.- or more dorso-central plates in the apical system is to be regarded as a 

 persistent embryonic character. In all other regular Urchins, a large dorso-central plate is early 

 developed, but becomes gradually resorbed. 



Peltastes, Ag. (Fig. 344, D). Ami straight or slightly flexuous, with simple 

 plates, and with small primary tubercles near the poriferous zones. I Amb 

 broad, with large, imperforate primary 

 tubercles, diminishing in size toward 

 the poles. Dorso-central plate small, 

 united to the large lateral basals, but 

 not touching the posterior one. Upper 

 Jura and Cretaceous. 



tiilcnia, Gray (Fig. 363). Test 

 small, globose, or depressed. Amb 

 plates simple. Dorso-central plate in 

 coiitact with all the basals ; radials 

 large, perforated at the adoral edge. 

 Cretaceous to Recent. ^mnr" FIG. 303. 



Goniophorus, Agassiz. Upper 

 Greensand. Heterosalenia, Cotteau. 

 Cretaceous. 



.li-rosalenia, Ag. (Fig. 364). Test depressed. Amb plates simple primaries 

 near the apical system, compound near the ambitus and actinally. lAmb 

 tubercles large, perforate, and crenulate ; those of the Amb much smaller, and 



Salenm scutigem, Gray. White Chalk ; Chareute 

 after Cotteau). A, Lateral and dorsal aspects of test 

 ./i. J5, Apical system, enlarged. 



Fio. 364. 



Acrosalenia temicidaroides, Wright. Middle Jura ; Stanton, Wiltshire. Dorsal, lateral, and ventral aspects 

 of test, i/, (after Wright). 



in two vertical rows. Periproct large, bounded anteriorly by the dorso-central, 

 which is in contact with the four large anterior basals. Spines cylindrical, 

 striated, or plain. Represented by numerous species from the Lias to the 

 Lower Cretaceous. 



Family 2. Hemicidaridae. Wright. 



Test thick, more or less spheroidal or sub-conical. Ambulacra increasing in 

 width actinally ; the pairs of pores in arcs actinally where the plates are compound ; 



