356 CRETACEOUS ECHINOIDEA. 



Family VIIL— ECHINOLAMPID^, WriffJd (p. 256). 



Test thin, oval, oblong, elevated or subdiscoidal, studded on upper and under surface 

 with small tubercles, often perforated on sunken areolae. Ambulacral areas large, peta- 

 loidal. Poriferous zones wide ; pores distant, united by sutures, and extending nearly to 

 the margin. Oral opening small, subcentral. Peristome with five prominent lobes and 

 well-developed petaloid concavities. Jaws absent. Apical disc very small, excentral, 

 and composed of four perforated genital and one imperforate plate, with five oculars 

 wedged into the circumference of the disc. Range of family, from Lower Oolites to the 

 existing period. One British Cretaceous genus : Pi"GURUs,with one species (pp. 256 — 260). 



Genus 21. — Pygurus, tV Orhi(;7iy (p. 257). 



Test large, discoidal or clypeoidal, rostrated posteriorly, furnished with small perfo- 

 rated tubercles on sunken areolse. Ambulacral areas strongly petaloidal. Poriferous 

 zones near the peristome crowded in triple oblique ranks. Oral opening pentagonal, 

 excentral. Peristome with five lobes and bays. Apical disc small. Anal opening oval 

 inframarginal, surrounded by a distinct area. Range of genus, from the Lower Oolites 

 to the Upper Greensand. One British Cretaceous species (pp. 258 — 260). 



Family IX.— SPATANGIDiE, cV OrUgny{^. 260). 



Test thin, oval or cordiform, covered with small perforated tubercles. Fasciole gene- 

 rally present. Ambulacral areas united at the summit. Anterior ambulacrum lodged in 

 a depression which extends to the anterior border. Oral aperture anterior, bilabiate. 

 Jaws absent. Apical disc with two or four genital pores, sometimes in proximity, some- 

 times apart. Ocular pores five, arranged pentagonally at the apices of the ambulacra. 

 Anal opening posterior and supramarginal, and closed by small plates. Spines hairlike. 

 Range of family, from the Cretaceous to the existing period. Five British Cretaceous 

 genera : Hemiaster, Epiaster, Micraster, Echinospatagus, and Enallaster, in 

 fifteen species (pp. 260 — 292). 



Genus 22. — Hemiaster, Besor (p. 261). 



Test thin, elevated, cordiform, ambulacral summit excentral and posterior. Fasciole 

 single, circumscribing the petaloid portions of the ambulacra. The pairs of ambulacra 

 petaloidal, unequal in length, and lodged in depressions, having large poriferous zones, with 



