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ORDER II EUECHINOIDEA—DIADEMATOIDA 
Family 1. Saleniidae. Desor (emend, Duncan and Sladen). 
Apical system large, with a persistent dorso-central plate or plates, which crowd 
the anal orifice somewhat out of the centre of the periproct. Ambulacra narrow, with 
numerous, simple, low primaries ; rarely compound actinally. Interambulacral plates 
few, with large tubercles. Teeth keeled. Spheridia present. Jura to Recent. 
The presence of one 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). Amb straight or slightly flexuous, with simple 
plates, and with small primary tubercles near the poriferous zones. [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. 
Salenia, Gray (Fig. 363). Test 
small, globose, or depressed. Aml 
plates simple. Dorso-central plate in 
contact with all the basals; radials 
large, perforated at the adoral edge. 
Cretaceous to Recent. 
Gontophorus, Agassiz. Upper Salenia scutigera, Gray. White Chalk; Charente 
Greensand. Heterosalenia, Cotteau. (after Cotteau). 4, Lateral and dorsal aspects of test 
1/;, B, Apical system, enlarged. 
Cretaceous. 
Acrosalenia, Ag. (Fig. 364). Test depressed. dmb plates simple primaries 
near the apical system, compound near the ambitus and actinally. LAdmb 
tubercles large, perforate, and crenulate ; those of the dmb much smaller, and 


Fic. 364. 
Acrosalenia hemicidaroides, Wright. Middle Jura; Stanton, Wiltshire. Dorsal, lateral, and ventral aspects 
of test, 1/; (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 ares actinally where the plates are compound , 
