BIHANG TILL K. SV, VET.-AKAD. HANUL. BAND 13. AKD. lY. N:0 O. 05 



Like the Coelopleuri the Echinocidaris uigra ^Iol., in 

 addition to its primary spinigeroiis tubercles, has, on tiie inter- 

 radia, from the ambitus upwards secondary miniite tubercles 

 forming on every interradial plate an upper transversc irrc- 

 arular row. and bears, all över, exceedino-lv numerous pedi- 

 cellarian tubercles. Thus tlie tubercular element is prevalent, 

 and the epistroma very much reduced. On the narrow ambu- 

 lacra, in brcadth 0,30 of the interradia, its protuberances, sub- 

 pedunculate and globulous, reddish and semi-transparcnt, are 

 seen forthcoraing singly or few in number in the rare inter- 

 stices left by the crowded pedicellarian tubercles; it crosses 

 the zones of pores, swelling into bosses, and on the upper 

 corner of the adjoining interradial plate forms a little group 

 of tumid irregular protuberances, while all along the plate it 

 is almost entirely excluded, until at the middle suture it again 

 comes forth as another similar group of protuberances. 



Such are, briefly stated, the appearances assumed by the 

 epistroma in the recent Arbaciad<e. Near to these come among 

 fossil forms the genera Dictyopleurus and Arachniopleurus of 

 DuNCAN and Släden'), approximating Coelopleurus, witli tvv^o 

 mar Ofinal ridjres on the ambulacra and two others, mesial, on 

 the interradia, all connecting by means of transversc and dia- 

 gonal ridnes, bearino- tubercles at the knöts, and more or less 

 distinctly noduled; the Glypticus'-) of Agassiz, with the luxu- 

 riant epistroma in exclusive posscssion of the upper test, with 

 large deformed bosses and vertical ridges, and the Codiopsis-') 

 described by Cotteau who figures its epistromal protuberances, 

 both apparently allied to Porocidaris; and the Coptechinus Cot- 

 teau*) and Progonechinus D. et Sl.^), reminding of A^j3acia. 

 Farther away from the Arbaciada? a compact epistroma is seen 

 in the Temnopleuridffi, in Salmacis and its allies, in Temno- 

 pleurus, Temnechinus, Opechinus, Trigonocidaris, extending 

 widely in various forms över great parts of the test, with the 



0—12. — C. Forbesi d'Arch., Duxc. et Slad. ib. V, p. 287, t. 46, fig. 1, 

 2, 4, 7, 9. Tert. Ech. Kachh and Kattywar, p. 53, t. 12, fig. 1. — C.^siu- 

 densis DUNC. et Slad. Foss. Ech. Sind, V, p. 298, t. 46, fig. 3, 5, 6, 8, 10; 

 t. 47, fig. 1, 2. 



') Fossil Echinoderras of Sind, p. 38, Pl. IX, fig. 1-3, 4, 5; X. fig. 

 5—8. — Ib. p. 42, Pl. IX, fig. 6—8. 



'-) Pal. Frän?., Jura, II, p. 574, Pl. 414-421. 



3) Pal. Frang. Jura, II, p. 571, Pl. 413. — Crét., VII, p. 774, Pl. 

 1189 — 1192. 



••) Bull. Soc. Zool. France, 1883. p. 456, Pl. 15, fig. 1—5. 



») Sind, p. 43, t. X, fig. 1—3. 



