GENEEA AND GROUPS OF THE ECHIlSrOIDEA. 85 



V. Family CTPHOSOMATiDiE. 



Test moderate in size, circular or subpentagonal in tumid 

 marginal outline, depressed, rarely subconical, highly orna- 

 mented ; plates moderate in number or numerous. 



Apical system very variable in size, shape, and structure, com- 

 pact, or with some or all radials intervening between the basals, 

 and the posterior basal intruding upon the posterior inter- 

 radium ; with the periproct posterior, and its plates either few 

 or numerous and hexagonal : arms posterior ; the madreporite 

 in the right anterior basal. 



Ambulacra with high compound plates, with from three to 

 seven pairs of pores in an arc ; near the apical system, and ex- 

 tending variously actinally, a biserial arrangement of the pairs, or 

 not ; pairs crowded or not at the j)eristome. The adoral and 

 supra-adoral components are primaries, and the others demi- 

 plates. Two vertical rows of primary tubercles. (Duncan, 1885, 

 Amb. Foss. Ech., Quart. Journ. Greol. Soc. p. 447.) 



Interradia usually depressed dorsally, with bare median spaces ; 

 rows of tubercles variable in number, larger than those of the 

 ambulacra. 



Peristome moderate and large, with branchial incisions. Spines 

 long and short, solid, some as needles ; striated longitudinally. 



This family subdivides with difficulty ; and the two groups of 

 it are not of subfamily value. 



Division I. 



Genus Cyphosoma. 



Subgenus Leiosoma. 

 Genus Coptosoma. 

 Gauthieria. 

 Thylechinus, 



Division II. 



Genus Micropsis. 



Subgenus Gagaria. 



Division I. 

 Species with and without a diplopodous poriferous arrange- 

 ment cannot be placed in the same genus ; and therefore only 

 the diplopodous species remain in the genus Cyphosoma as 

 now constituted. Moreover, the genus now includes the species 

 with the apical system encroaching upon the posterior inter- 

 radium. Cotteau has found the details of the apical system; and 



