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OOLITIC ECHINODERMATA. 
ovarian and five ocular plates, the right lateral plate large, and supporting a prominent 
spongy madreporiform body. Spines small, short, and covered with microscopic lines. 
The Echinoconidse range from the Lias to the existing period. Four British Oolitic 
genera (Holeotypus, Pygaster, Hyboclypus, and Galeropygus), with thirteen 
British Oolitic species. 
Genus 14. — Holeotypus, Desor (Vol. I, p. 259). 
Test thin, circumference circular, more or less hemispherical, depressed, always tumid 
at the sides, flat or concave at the base. Ambulacral areas narrow and lanceolate, 
bearing six to eight rows of small tubercles from base to apex. Interambulacral wide, 
supporting numerous small perforated tubercles, arranged in vertical and concentric 
rows. Poriferous zones narrow; pores unigeminal throughout. Oral opening very large, 
circular, in centre of base. Peristome divided into ten equal lobes. Jaws present. Anal 
opening very large, inferior, infra-marginal, rarely marginal, sometimes occupying the entire 
space between the oral opening and the border. Apical disc nearly central and ; vertical. 
The genus is found in the Oolites and Lower Cretaceous beds. Three British Oolitic 
species (Vol. I, pp. 260—268). 
Genus 15. — Pygaster, Agassiz (Vol. I, p. 273). 
Test thick, subpentagonal, more or less elevated, convex on upper surface, concave on 
under. Ambulcaral areas narrow, bearing four to six rows of small tubercles, the 
marginal rows extending from base to apex. Interambulacral wide, bearing small, 
nearly equal-sized, perforated, and uncrenulated tubercles, arranged in vertical and hori- 
zontal rows, of which the two are median, and continuous throughout. Poriferous zones 
narrow ; pores unigeminal throughout. Oral opening circular. Peristome deeply notched 
and marked by ten equal lobes. Jaws present. Anal opening very large, oblong, superior, 
and almost universally continuous with apical disc. Apical opening central, large. 
Spines small, short, covered with minute longitudinal lines. Range of genus from 
the Lias to the existing period. Pive British Oolitic species (Vol. I, pp. 275 — 282,. 
463). 
Genus 16. — Hyboclypus, Agassiz (Vol. I, p. 291). 
Test thin, subcircular or subovate, upper surface unequally elevated, the anterior 
half usually higher than the posterior half. Under surface concave or undulating. 
Ambulacral areas narrow, flexuous, and disjointed at summit by the length of the apical 
disc. Three terminate at the oral extremity of the apical disc, two at the opposite end. 
