SUMMARY. 



173 



Gems 3. — Diplocidaris, Desor (Vol. I, p. 56). 



Test thick, large, depressed. Pores arranged in double oblique pairs. Genus found 

 in the Liassic and Oolitic strata. Two British Liassic and Oolitic species (Vol. I, 

 pp. 56—58, 452). 



Family II.— HEMICIDARIDtE, Wric/Jd (Vol. I, p. 68). 



Test thick, spheroidal, more or less depressed. Genital plates sometimes bearing 

 perforated tubercles. Ambulacral areas, narrow, straight, or undidating, and carrying 

 perforated semi-tubercles. Interambulacral areas wide, bearing large tubercles, generally 

 perforated and raised on prominent bosses. Poriferous zones narrow and undulated ; 

 pores small, contiguous, and unigeminal, except near the peristome, where they are 

 bigeminal and trigeminal. Primary spines generally long, cylindrical, and tapering, 

 sculptured with lines, and generally without asperities. Mouth and anal opening 

 large. Peristome divided by notches into five large and five small lobes. Jaws present. 

 Range of family from the Oolitic to the Tertiary strata. Family represented in the British 

 Oolitic strata by one genus, Hemicidaris, Thirteen British Oolitic species. 



Gems 4. — Hemicidaris, Agassiz (Vol. I, p. 69). 



Test thick, generally flattened at base. Ambulacral areas more or less undulating, 

 bordered by minute tubercles, and supporting on the lower part, for about a quarter of 

 the whole length, perforated tubercles, which increase in magnitude from below upwards, 

 and on the other three quarters minute perforated tubercles. Thirteen British Oolitic 

 species (Vol. I, pp. 69—100, 453). 



Family III.— DIADEMADtE, Wright, (Vol. I, p. 106). 



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

 areas 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 either primary, of equal size, 

 in two to eight rows, perforated, or with two to four rows of secondary tubercles. Pori- 

 ferous zones narrow, and almost always straight ; pores unigeminal, bigeminal, or tri- 

 geminal. Oral and anal opening large. Apical disc small. Peristome decagonal, 

 generally deeply notched. Spines cylindrical, solid or tubular ; those of the fossil not 



