42 PEOF. p. M, dtjncan's revision of the 



Interradia with numerous coronal plates which are low, broad, 

 and imbricating more or less, and with four vertical rows of plain 

 primary tubercles at the ambitus, resembling those of the ambu- 

 lacra, and diminishing in number and size actiually and abactinally, 

 some secondary tubercles. 



Peristome large ; branchial notches deep. Jaws powerful, with 

 grooved teeth. Spines small, hollow, longitudinally striated. 

 Pedicellarise small, tridactyle around the peristome, gemmiform 

 orally, large tridactyle aborally. 



Fossil. Oolite: England. 



The above generic definition has been taken mainly from Mr. 

 Grroom's admirable description of the solitary species. 



Subfamily JEchinothurince (p. 41). 



G-enus Echinothueia, 8. F. Woodward, 1863, Geologist, vol. vi. 

 pp. 327-330. Wright, 1870, Fal. Soc.,Frit. Foss.Ech. Cret. 

 Form. p. 124. 



Test large, plates imbricating, in both areas and in opposite 

 directions. Apical system wanting. 



Ambulacra wide at the ambitus, narrower towards the peri- 

 stome ; plates rather high ; complete overlap of the adoral edge 

 of one plate upon the corresponding aboral edge of the actinally 

 placed plate, no space left ; overlap of the outer edges of the 

 plates by the interradial plate edges. A pair of pores in a primary 

 plate and two pairs in small demi-plates in the position of the 

 adoral suture. Buccal plates imbricating and perforated, ambu- 

 lacral only. Tubercles small and scanty. 



Interradia with larger plates, each in contact throughout its 

 breadth with the plate above and actinally, and overlapping in the 

 contrary direction to the ambulacral plates. Tubercles rare, not 

 large, perforated, the same actinally as dorsally. Spines cylin- 

 drical, striated, with a milled ring. Jaws stout. Ornamentation 

 scanty, and similar actinally and dorsally. 



Fossil. Upper Cretaceous : England. 



Genus Phoemosoma, Wy. Thomson, 1873, FMl. Trans. Boy. Soc. 



vol. clxiv. pt. 2, p. 732 (1874). A. Agassiz, 1881, Heport on 



' Challenger ' Echini, p. 91 ; Fejport on ' Blake ' Eccped. Echini, 



1883, p. 35. 



Test small to large, thin, more or less flexible, tumid or 



depressed dorsally, flat actinally, circular or polygonal in ambital 



