172 
OOLITIC ECHINODERMATA. 
recent period, and are represented in the British Liassic and Oolitic strata by nine families, 
twenty-one genera, and 120 species, and are divisible into two (A and B) sections, the 
ECHINOIDEA ENDOCYCLICA and the ECHINOIDEA EXOCYCLICA. 
Section A— Echinoidea endocyclica, WHc/Jd (Vol. I, p. 17). 
Anal opening luitJiin the genital plates, always opposite the mouth. Jaws always 
present. 
The section contains five families : CiDAHiDiE, HEMiciDARiDiE, DiADEMADiE, 
EcHiNiD^, and Saleniad^, ranging from the Trias to the existing period. The five 
families are represented in the British Liassic and Oolitic strata, and give thirteen genera 
and eighty-two species. 
Family I.— CIDARIDtE, TFriyht (Vol. I, p. 23). 
Test thick, spheroidal, generally depressed at the upper and the under surfaces. 
Ambulacral areas narrow, usually undulating, and destitute of primary tubercles. Inter- 
ambulacral areas wide, carrying a few large primary perforated tubercles. Poriferous 
zones narrow, straight; pores generally unigeminal. Oral and anal openings large. 
Peristome destitute of notches. Jaws present. Primary spines long, massive, and more 
or less cylindrical. Family ranging from the Trias to the present period, and represented 
in the British Liassic and Oolitic strata by three genera : Cidaris, Rabdocidaeis, and 
DiPLOCiDARis, with fifteen species. 
Genus 1. — Cidaris, Klein (Vol. I, p. 25). 
m 
Test thick, more or less depressed. Ambulacral areas undulating. Primary 
tubercles few, rarely more than six in a row. Miliary zones more or less wide. Pores 
of the poriferous zone unigeminal and contiguous. Range of genus from the Trias to 
the recent period. Eleven British Liassic and Oolitic species (Vol. I, pp. 26 — 53, 451). 
Genus 2. — Rabdocidaris, Besor (Vol. I, p. 54). 
Test thick, slightly depressed. Ambulacral areas nearly straight. jMiliary zones 
wide. Pores unigeminal, not contiguous, but connected l)y a small horizontal furrow. 
Range of genus from the Liassic to the Lower Cretaceous beds. Two British Liassic and 
Oolitic species (Vol. I, pp. 54, 55). 
