348 CRETACEOUS ECHINOIDEA. 



crenulated tubercles. Interambulacral areas marked at ambitus by six to ten lines of per- 

 forated and crenulated tubercles, decreasing in number above and below until only two 

 lines remain. Poriferous zones wide and straight; the pores bigeminal throughout, and 

 forming at the upper surface and ambitus two distinct rows, becoming blended together 

 at the inframarginal region and remaining conspicuous at the base. Oral opening sub- 

 circular and lobed. Apical disc small. Spines unknown. The genus is only met with 

 in the Cretaceous strata. One British Cretaceous species (pp. 114 — IIG). 



Genus 4. — Echinocyphus, Cotteau (p. IIG). 



Test thin, small, circular, more or less inflated on the upper surface, concave at the 

 base. Ambulacral areas rather wide, furnished with one, rarely two, rows of primary 

 tubercles. Interambulacral areas with two rows of tubercles. Tubercles of both areas 

 of nearly the same size, alternate, crenulated, but not perforated. Interambulacral plates 

 of base sculptured, with more or less strongly marked sutural depressions, and exhibiting 

 on their surface a border of radiating mihary granules. Poriferous zones nearly straight, 

 narrow ; pores unigeminal. Oral opening moderately large, subcircular, provided with 

 slight lobes. Anal opening of same size. Apical disc unknown. Spines unknown. 

 The genus is only met with in the Cretaceous strata. Two British Cretaceous species 

 (pp. 116—119). 



Genus 5. — Glyphocyphus, Haime (p. 120). 



Test thin, small, circular, more or less inflated above, concave below. Ambulacral 

 areas somewhat narrow, generally with two rows of alternate tubercles, sometimes with 

 only one row. Interambulacral areas with two rows of alternate tubercles. Tubercles of 

 both areas of nearly the same size, crenulated and perforated. Ambulacral and interam- 

 bulacral plates marked by sutural depressions ; surface around the tubercles covered 

 with tine, close-set, homogeneous granules. Poriferous zones straight, narrow ; pores 

 unigeminal. Oral opening small, subcircular, divided into lobes by feeble incisions. 

 Anal opening not large, subpentagonal. Apical disc small, solidly united to the test, 

 forming an elongated oval ring. Spines unknown. The genus confined to the 

 Cretaceous strata. One British Cretaceous species (pp. 121 — 124). 



Genus 6. — Cyphosoma, Agassiz (p. 128). 



Test thick, moderate in size, circular or subpentagonal. Sides slightly inflated, 

 depressed, convex above, flattened below. Ambulacral areas furnished with two rows 

 of prominent crenulated and imperforate primary tubercles. Interambulacral narrow 



