354 CRETACEOUS ECHINOIDEA. 



Family VIL— ECHINOBRISSID^, Wric/M (p. 240). 



Test thin, circular, oblong, siibpentagonal or clypeiform, covered with microscopic 

 perforate or imperforate tubercles surrounded by excavated areolae. Ambulacral areas 

 narrow. Poriferous zones more or less petaloid, pores set at different distances apart, 

 and united by connecting sutures. Interambulacral areas wide. Oral opening small, 

 nearly central, pentagonal. Peristome generally lobed. Jaws absent. Apical disc 

 small with four perforate and one imperforate genital plates ; ocular plates very small. 

 Madriporiform body extending into the centre of the disc. Anal opening in a furrow 

 in upper margin or under surface of the single interambulacrum. Range of the family, 

 from the Oolitic to the existing period. Eive British Cretaceous genera : Catopygus, 

 Clypeopygus, Echinobrissus, Trematopygus, Caratomus, and eight species (pp. 

 241—256). 



Genus 16. — Catopygus, Agassiz (p. 240). 



Test thin, oval or elongated, convex above, flat below, sides inflated, aual half much 

 higher than oral half. Ambulacral areas narrow, petaloid above, forming a straight band 

 on under side. Poriferous zones composed of an inner series of round pores, and an 

 external series of elongated pores arranged in conjugate pairs ; tubercles very small, 

 numerous and scattered. Oral opening small, subcentral, pentagonal, with five pro- 

 minent lobes. Apical disc small at the summit, prominent, with four perforated ovarial 

 plates, and five microscopic ocular, the madriporiform body projecting. Anal opening 

 small, round or oval, situated in the posterior border, at the summit of the vertical trun- 

 cation of the posterior border. Spines unknown. Range of genus, from the Lower 

 Greensand to Upper Tertiary. Three British Cretaceous species (pp. 241 — 246, 340). 



Gems 17. — Clypeopygus, d'OrUgny (p. 246). 



Test thin, oblong, depressed, convex above, concave below, covered with numerous 

 small tubercles which are larger on the under side than the upper, and are placed in 

 areal depressions. Ambulacral areas narrow and subpetaloid on upper surface, narrow 

 below, and suddenly contracting near the peristome. Poriferous zones unequal in width 

 from summit to base. Interambulacral area wide. Oral opening excentral nearest the 

 anterior border. Peristome pentangular, surrounded by five rosettes of buccal pores, and 

 separated by five prominent lobes. Apical disc small, excentral, and composed of four 

 perforated and one imperforate genital plates, the right antero-lateral supporting the 

 madriporiform body, which extends into the middle of the disc and forms a prominence 

 there. A Lower Cretaceous genus. One British Cretaceous species (pp. 247, 248). 



