GENERA AXD aUOUPS OF THE ECeiSTOIDEA. 79 



crenulate and perforate primary tubercles ; poriferous zones 

 broad ; plates compound, large, high, composed at tbe ambitus 

 and actinally of two sets of triplets, each consisting of low, broad 

 primaries, sometimes wdtb ademi-plate, wntb their sutures curved, 

 convexity towards the tubercles ; pairs of pores iu oblique sets of 

 three pairs, really in close triplets, the adoral pair of a compound 

 plate being nearest the ambulacral median line and the aboral 

 the most remote. 



Interradia with a broad median area abactinally, elsewhere 

 with several rows of crenulate and perforate primaries, slightly 

 larger than those of the ambulacra, each with a large flat scrobicule. 

 Coronal plates rather numerous, low and broad, overlapping more 

 or less, pitted iuside and some split longitudinally or not. 



Peristome variable ia size ; branchial cuts large ; membrane 

 with plates, the largest carrying spines. Jaws small ; teeth 

 grooved. Larger spines about one half of the diameter of the 

 test, striated, verticillate. 



Recent. Panama, Gulf of California, Zanzibar, Philippines, 

 East-Indian Islands. 



Genus PoLTCTPntrs, Agassiz, 1846, Gat. Hais. des EcJi., Ann. d. 

 Sci. Nat. ser. 3, vol. vi. p. 361. Desor, 1858, Synopsis, p. 117. 

 Cotteau, 1863, Bev. et Mag. de Zool. ser. 2, vol. xv. p. 261. 



Test small, subcorneal or hemispherical dorsally, tumid at the 

 circular ambitus, rather flat actinally. 



Apical system small ; basal plates large and united ; periproct 

 oblique or not. 



Ambulacra straight, rather wide, with rather broad poriferous 

 zones, which may be sunken ; pairs of pores in close and very 

 oblique triplets, triserial abactinally and polyserial actinally ; 

 plates low, compound, " diadematoid." Tubercles of the inter- 

 poriferous areas small, plain, in four or more vertical rows, the 

 outer the larger. 



Interradia with numerous low broad plates, each with two 

 horizontal rows of numerous plain tubercles, resembling those 

 of the ambulacra ; but one row has small tubercles ; usually the 

 tubercles increase in size actinally ; vertical row^s five or more in 

 number. 



Peristome large, decagonal ; ambulacral lips large ; branchial 

 incisions well developed. 



Fossil, Oolite : England and Europe. 



