174 



OOLITIC ECHINODERMATA. 



longer than the diameter of the shell ; surface of the solid forms covered with very fine, 

 minute longitudinal striae ; and that of the tubular with oblique annulations of fringe-like 

 scales. Jaws present. Range of family from the Trias to the existing period. Family 

 represented in the British Liassic and Oolitic strata by four genera : Pseudodiadema, 

 Hebiipedina, Heterocidaris, and Pedina, in thirty-four species. 



Genus 5. — Pseudodiadema, Desor. (Vol. I, p. 108). 



Test moderately thick, not large. Arabulacral areas one third to one half the width of 

 the interambulacral. Ambulacral areas furnished with two rows of primary tubercles. 

 Interambulacral areas sometimes provided with two rows of primary tubercles, sometimes 

 showing four or six rows of equal-sized tubercles at the equator. Pores of poriferous 

 zones unigeminal throughout, or bigeminal in the upper part of the zones. Apical disc 

 small. Oral opening large. Peristome deeply notched. Spines solid, cylindrical or 

 needle-shaped, short, and covered longitudinally with very minute microscopic lines. 

 Range of genus from the Lias to the Cretaceous beds. Thirteen British Liassic and 

 Oolitic species (Vol. I, pp. 110—132, 456). 



Genus 6. — Hemipedina, Wrigld (Vol. I, p. 143). 



Test thin, much depressed on the upper surface, and flat or slightly concave on the 

 lower surface. Ambulacral areas narrow. Interambulacral areas usually double the 

 width of the ambulacral, with two to eight rows of perforated tubercles at the equator, 

 having uncrenulated bosses ; upper part of miliary zone wide and covered with fine granu- 

 lations. Pores of poriferous zones unigeminal. Spines slender and needle-shaped. Range 

 of genus from the Lias to the Oolites. Eighteen British Liassic and Oolitic species 

 (Vol. 1, pp. 144—167, 457). 



Genus 7. — Heterocidaris, Cotteau (Vol. I, p. 455). 



Test thin, large, circular, depressed on the upper surface, almost flat on the lower 

 surface, Ambulacral areas very narrow, furnished with two rows of small distinct per- 

 forated tubercles, uniform in size, and raised on small bosses placed in regular rows. 

 Interambulacral areas very wide, provided with from six to eight rows of large, nearly 

 equal-sized perforated tubercles, raised on prominent bosses with crenulated summits. 

 Miliary zone finely granulated. Poriferous zones narrow ; pores small, non-conjugate, 

 having a slight disposition to a trigeminal arrangement near the oral opening. Oral 

 opening large, pentagonal, and lobed. Anal opening circular. Spines long and cylindrical. 



