SUMMARY. 353 



. Gemcs 14. — Holectypus, Desor (p. 231). 



Test thin, circular or subcircular, more or less hemispherical, conical or subconical, 

 always tumid at the sides and flat or concave at the base. Ambulacral areas narrow, 

 straight, lanceolate, with six or eight rows of small, perforated and crenulated tubercles, of 

 which the marginal series only extend from the base to the apex. Poriferous zones narrow, 

 pores unigeminal throughout. Interambulacral areas wide, furnished with small 

 perforated and crenulated tubercles. Interambulacral plates not carrying on the inner 

 surface projecting plates. Oral opening circular, central. Peristome notched. Jaws 

 present. Apical disc central, vertical, composed of five ovarial and five ocular plates. 

 The right antero-lateral much the larger and supporting a prominent madriporiform 

 body. In Oolitic species, anterior and posterior plates perforated, and single plate 

 imperforate ; in Cretaceous species all the plates perforated. Anal opening large, 

 infraraarginal rarely, marginal sometimes occupying the centre space between peristome 

 and border. Spines short, longitudinally striated. Range of genus, from the Inferior 

 Oolite to the Lower Chalk. One British Cretaceous species (pp. 233, 234). 



Family VI.— ECHINONIDtE, Wright (p. 234). 



Test thin, oval, or round, depressed. Ambulacral areas small, lanceolate. Inter- 

 ambulacral wide. Plates of both areas furnished with small, equal-sized imperforate 

 and noncrenulate tubercles. Oral opening subcentral, irregularly pentagonal. Jaws 

 absent. Apical disc nearly central, four ovarial plates perforated, one imperforate. 

 Anal opening oblong, pyriform, basal or mai-ginal closed by plates. Range of family, 

 from the Cretaceous rocks to the existing period. One British Cretaceous genus : Pirina, 

 and three species (pp. 235 — 239). 



Genus 15. — Pyrina, Besmoulins (p. 235). 



Test thin, oval or round, depressed or globular; under surface inflated and often 

 depressed around the mouth opening. Ambulacral areas moderately narrow, lanceolate. 

 Interambulacral areas wide. Both areas covered with small equal-sized and imper- 

 forate tubercles. Poriferous zones straight and narrow, pores in regular pairs. Oral 

 opening oval, oblique, subcentral. Peristome destitute of lobes. Apical disc small, sub- 

 central, with four perforated genital plates. Anal opening oval and marginal, generally 

 nearer the upper than the under surface. Spines unknown. Three British Cretaceous 

 species (pp. 236—239). 



