60 PEOF. p, M. dfncan's eeyisiojt op the 



I. Subfamily Diadematince (p. 59). 



Genus Diadema, Scbynvoet, 1711, TTies. Imag. Pise. Sfc. p. 2, 

 pi. xiv. Gray, 1825, Ann. Phil. vol. xxvi. p. 426. Peters, 

 1853, AbJiandl. k. Akad. Wiss. Berlin (1854), p. 107. Bolsclie, 

 1865, Archiv Jiir Naturg.YoY. xxxi. p. 325. A.Agass. 1874, 

 Pevision, p. 274. Puncan Sf Sladen, 1885, Jburn. Linn. Soc. 

 (Zool.),vo\. xix. p. 95. Loven, 1887, On Species ofPcJi. desc. ly 

 Liiinodus, PiTiang till K. SvensJca Vet.-Alcad. Handl. Bd. xiii. 

 Afd. iv. No. 5, pp. 125-137. Sarasin, P. Sf P., 1887, 

 Prgebn. Naturw, Porsch. auf Ceylon, Bd. i. Heft 1, pp. 1-17. 

 Syn. Pseudodiadet7ia,J)esor-, Tetragramma, Agass. ; Hehertia, 



Mich. 



Test thin, moderate in size, circular or slightly polygonal in 

 tumid marginal outline, wider than liigh, rather depressed. 



Apical system sunken or not, large ; basal plates large, with a 

 long outer angle and large duct-perforation ; radial plates small 

 and some may enter the periproctal ring. Periproct large, with a 

 thin membrane furnished with a few plates near the ring. Anal 

 orifice at the end of a tube. 



Ambulacra straight, narrow, often projecting ; pairs of pores 

 in simple series in arcs ; plates compound, each with a middle 

 broad primary component carrying a tubercle and occupying 

 much of the median sutural edge, having a long low primary 

 above and below and occupying but little of the median sutural 

 edge, the edges of these plates curved, convexity towards the 

 base of the tubercle on the middle plate. Two vertical rows of 

 small, primary, crenulate and perforate tubercles extending from 

 peristome to apex. 



Interradia with a bare median space near the apex or not ; 

 coronal plates long and low. Primary tubercles in two or more 

 rows, resembling those of the ambulacra in structure, but larger ; 

 secondary tubercles and granules on the flanks of the scrobicules. 



Peristome large, decagonal ; branchial incisions with " tags." 

 Actinal membrane thin, but slightly plated. Perignathic girdle 

 with well-developed ridges ; processes united and rather tall, a 

 projection of the test beyond the ridges into the peristome. Jaws 

 large ; pyramids with a tall foramen open above ; teeth grooved. 

 Eye-spots numerous. Spines long, hollow, closely verticillate, 

 striated longitudinally, milled ring prominent. 



Fossil. Lias, Oolites, Cretaceous : England, Europe, JST. Africa, 

 Egypt, Asia, N. America. Eocene : Europe. 



