SUMMARY. 347 



poriferous zones unigeminal and contiguous. Range of genus, from the Trias to the , 

 existing period. Seventeen British Cretaceous species (pp. 36 — 79). 



Family II.— DIADEMADtE, WrigU (p. 80). 



Test in general moderately thick, subpentagonal, more or less depressed. Ambulacral 

 areas almost always straight, more or less wide, furnished with two or four rows of 

 tubercles often as large as those of the interambulacral. Interambulacral areas equal to, 

 or double as wide as, the ambulacral. Tubercles of the interambulacral areas crenulated 

 or non-crenulated, either primary, of equal size, in two to eight rows, generally perforated, 

 or with two or four rows of secondary tubercles, much smaller in size, filling up the 

 interspaces of the area. Poriferous zones narrow and almost always straight ; pores 

 imigeminal, bigeminal, or trigeminal. Oral and anal openings usually large. Peristome 

 strongly decagonal, generally deeply notched. Spines cylindrical, solid or tubular. 

 Those of the fossil not longer than the diameter of the shell ; surface of the solid forms 

 covered with very fine minute longitudinal striae ; and those of the tubular with oblique 

 annulations of fringe-like scales. Jaws large. Range of family, from the Trias to the 

 existing period. Family represented in the British Cretaceous strata by five genera : 

 PsEUDODiADEMA, Pedinopsis, EcHiNOCYrHUs, Glyphocyphus, Cyphosoma, and by 

 twenty-three species (pp. 87—124, 341, 342). 



Genus 2. — Pseudodiadema, Desor (p. 86). 



Test moderately thick, generally not large. Ambulacral areas one third to one half 

 the width of the interambulacral. Ambulacral areas furnished with two rows of primary 

 tubercles. Interambulacral areas sometimes provided with two rows of primary tubercles, 

 sometimes with two rows of primary and two to four short rows of smaller secondary 

 tubercles, sometimes with four or six rows of nearly equal-sized primary tubercles at the 

 equator. Primary tubercles of both areas perforated, having sharply-crenulated summits. 

 Poriferous zones narrow and straight ; pores of poriferous zones unigeminal throughout, or 

 bigeminal in the upper part of the zones. Oral opening large. Peristome deeply notched. 

 Anal opening pentangular. Spines solid, cylindrical or needle-shaped, short, and covered 

 longitudinally with very minute microscopic lines. Range of genus, from the Lias to the 

 Upper Cretaceous beds. Twelve British Cretaceous species (pp. 87 — 113, 341, 342). 



Genus 3. — Pedinopsis, Cotteau (p. 1 1 3). 



Test thin, of moderate size, inflated, sometimes subconical. Ambulacral areas rather 

 wide, fm-nished with two complete and two incomplete rows of small perforated and 



