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, Wri^Jd (Vol. I, p. 17). 



Anal opening within the genital plates, always opposite the mouth. Jaws always 



present. 



The section contains five families : Cidarid^, HEMiciDARiDiE, Diademad^b, 

 EcHiNiD^, and SALENiACiE, 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.— CIDARID^, Wright (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, Rabdocidaris, and 

 DiPLOCiDARis, with fifteen species. 



Genus 1. — Cidaris, Klein (Vol. I, p. 25). 



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, shghtly depressed. Ambulacral areas nearly straight. Miliary zones 



wide. Pores unigeminal, not contiguous, but connected by 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). 



