58 PEOF. p. M. DTJlSrCATSr's EETISIOIir OF THE 



and the one founded by Desor, which in the first instance was 

 called by the same name as the recent forms {Diadema by Gray), 

 are that there is no verticillation of the longitudinally striated 

 spines of JPseudodiadema, and the spiues are solid in the fossil, 

 hollow in the recent form. These are possibly specific characters 

 at the most, and hence one of the first steps in a revision 

 must be the elimination of Pseudodiadema, with its host of 

 species. 



IV. Family DiADEMATiDiE *. 



Regular ectobranchiate gnathostomes, with or without rudiments 

 of internal branchiae, with highly ornamented, tumid, depressed, 

 or spheroidal tests ; with a weJi-developed dorso-central system, 

 often with a tubular anal orifice ; with the madreporite in the 

 right anterior basal. 



Ambulacra moderately broad or narrow, straight, flash or tumid, 

 with vertical rows of primary tubercles resembling the interradial 

 but usually smaller ; pairs of pores either in simple series, or in 

 arcs, or in two or more vertical series ; the plates compound near 

 the ambitus and actinally, low and numerous ; the median com- 

 ponent carrying the tubercle and reaching the median line, and 

 therefore a large primary plate, and the adoral and aboral plates 

 of the compound low, broad primaries, smaller than the median 

 plate and having their sutural lines curved towards the tubercle 

 of the median component ; demi-plates rarely exist. 



Interradia broad, with numerous low plates, with vertical rows 

 of primary tubercles, and sometimes with more than one horizontal 

 row of them on a plate ; vertical rows varying in number, dimi- 

 nishing dorsally ; tubercles resembling those of the ambulacra, 

 but usually larger. 



Peristome large, polygonal, with branchial incisions. Peri- 

 gnathic girdle continuous ; processes arched and the ridges low. 

 Jaws without a closed pyramidal foramen ; teeth grooved. Ten- 

 tacles heteropodous. Spheridia present. Spines variable, short 

 or long, hollow, striated and grooved longitudinally, verticillate 

 or not, (solid from fossilization) . 



* The definition is an amendment of Gray, 1835 ; Peters, Abhandl. d. konigl. 

 Akad. d. Wiss. Berlin, read 1853, published 1855, p. 106 ; A. Agassiz, 1874. 

 For morphology see Quart. Journ. G-eol. Soe. 1885, p. 419, Journ. Linn. Soc. 

 vol. yix. 1885, pp. 95 and 201. Also P. and P. Sarasin, Ergebn. Naturw. Forsch. 

 auf Ceylon, 1884-6, published 1887, Ed. i. Heft 1, pp. 1-17. 



