SUMMARY. 351 



perforated, rhomboidal ovarial plates, and five cordate oculars, much granulated. 

 Periprocte small. Spines unknown. Range of genus, from the Upper Greensand to the 

 existmg period. One British Cretaceous species (pp. 187 — 189). 



Family IV.— ECHINOTHURIDtE, Wyv. Thomson. 



Test thin, circular, flexible, plates more or less overlapping, those of the ambulacral 

 areas imbricating from below upwards, those of the interambulacral from above down- 

 wards. Under and upper sides sometimes very different. Ambulacral and inter- 

 ambulacral areas carrying primary perforated tubercles, and scattered secondary tubercles 

 and granules. Poriferous zones with three pairs of pores. Oral and anal openings large. 

 Oral opening protected by scale-hke plates. Jaws strong. Spines thin, hollow, with 

 projecting processes arranged in an imperfect spiral. Range of family, from the 

 Cretaceous to the existing period. One British Cretaceous genus (Echinothuria) and 

 one species. 



Genus 11. — Echinothuria, Woodward (^. 124). 



Test circular; depressed, plates slightly overlapping. Ambulacral plates narrow, long, 

 imbricating from the anal aperture towards the oral aperture. Interambulacral plates 

 arranged in the reverse order. Ambulacral plates containing two smaller plates, each 

 perforated by a pair of pores intercalated in a notch in the middle of the lower margin, 

 and perforated by a third pair of pores nearer the interambulacral areas. Primary 

 tubercles of the ambulacra perforated, few, and irregularly distributed. Alternate plates 

 of the interambulacral areas bearing one perforated primary tubercle. Oral opening large. 

 Spines small, slender, striated, fringed. One British Cretaceous species (pp. 125 — 127). 



Section B.— Echinoidea exOCyclica, Wrigld (p. 29). 

 Anal opening outside the genital plates ^ never opposite the mouth. 

 The section contains eight families : EcHiNocoNiDiE, Collyritid^, Echinonid^, 



ECHINOBRISSID^, EcHINOLAMPID^, CLYPEASTERIDiE, ECHIJ^OCORII)^, SpATANGID^, 



and ranges from the Liassic to the existing period. Six families (Echinoconid^, 

 Echinonid^, Echinobrissid^, Echinolampid^, Spatangid^, Echinocorid^), are 

 represented in the British Cretaceous strata by nineteen genera : Discoidea, Echino- 

 coNus, HoLECTypus, Pyrina, Catopygus, Clypeopygus, Echinobrisstjs, Trema- 

 TOPYGUs, Caratomus, Pygurus, Hemiaster, Epiaster, Micraster, Echinospatagus, 

 Enallaster, Cardiaster, Infulaster, Holaster, Echinocorysj and by fifty-four 

 species. 



