GENERA AND GBOUPS 0:F THE ECHINOIDEA. 133 



Apical system large, madreporite large and in the usual basal 

 plate ; some radial plates entering and separating basals ; peri- 

 proct large, its plates numerous, small, tuberculate, and spine- 

 bearing. 



Ambulacra very wide, nearly equalling the interradia in breadth, 

 and the widest at the peristome ; poriferous zones very broad ; 

 the pairs of pores large, triserial, very close vertically and dis- 

 tant horizontally, the inner and the outer rows very persistent 

 and vertical, the middle row somewhat variable in the direction 

 of the pairs of pores ; small primary tubercles amongst the series 

 of pairs ; the plates very low and numerous, broad, compound ; 

 the adoral constituent with the inner pair of pores is a primary 

 plate which is low in the poriferous zone, and occupies all the 

 interporiferous part of the compound plate ; the next plate above 

 is a demi-plate with the outer pair of pores, and the upper com- 

 ponent is a broad demi-plate with the middle pair of pores. The 

 compound plates may join and two produce a large one, and the 

 primary plate of the upper component may be formed into a 

 demi-plate. Interporiferous areas with several vertical rows of 

 small primary tubercles plain and imperforate. 



Interradia with very numerous coronal plates and many, some- 

 what distant, vertical rows of primary and secondary tubercles 

 resembling those of the ambulacra. More or less bare median 

 areas in the ambulacra, and especially in the interradia abactinally ; 

 the angles of the sutures slightly pitted. 



Peristome comparatively small, with a tumid surface beyond, 

 the branchial incisions large and long ; perignathic girdle with 

 low ridges, and very tall slender oblique processes, uniting largely 

 above ; arch large. Jaws high, with a large foramen, teeth keeled. 

 Spines short, sharp, striated. Peristomial membrane with ten 

 large plates and other small ones. 



Fossil. Miocene : Europe ?, "W. Sind, Asia. 



Becent. Grulf of Suez, Eed Sea, E. coast of Africa, Mauritius, 

 Eodriguez, Masbate, Philippines, Japan, East Indian Islands, 

 Gulf of California, Caribbean Sea to Bermuda. 



Subgenus Evechinus, Verrill (genus), 1871, Notes on BacUata, 

 p. 583 ; 1871, Trans. Connect. Acad. vol. i. no. 8. A. Agassiz, 

 1872-74, Bevision, p. 502. 

 Coronal plates moderate in number, the branchial incisions 



