304 ECHINtx IYAMUS PUSILLUS. 



CLYPEASTRIDAE. 



Suborder Clypeastridae Auass. 1836. Prod. Mon. Rad. 



EUOLYPEASTRIDAE. 



Family Euolypeastridae Hakckel, 1866. Generclle Morph. 



FIBULARINA. 



Subfamily Fibularina Gray, 1855. Cat. Rec. Ech. (emend.) 



ECHINOCYAMUS. 



Echinocyamus Van Piikl. 1771. Rrief. 



Small flattened Sea-urchins with a thick test. The ambulacra are very 

 imperfectly petaloid, poriferous zones diverging or parallel, pores discon- 

 nected. The horizontal sutures of the ambulacra! plates extending to the 

 actinostome, pierced with a large number of pores, the pores most numer- 

 ous above the ambitus. The interior of test has simple radiating partitions 

 extending towards the central actinostome. The supports of the jaws (auri- 

 cles) very tall and broad. Ambulacra broader than the interambulacra ; 

 tubercles of uniform size, extending over apical rosette; pores of madreporic 

 body frequently as large as genital or ocular openings. Spines short, 

 slender; anus inframarginal, situated near actinostome; genital pores four 

 in number, small, indistinct; ocular pores large. 



Echinocyamus pusillus 



Spatagus pusillus MiJIX. 1776. Prod. Zool. Dan. 

 ! Echinocyamus pusillus Gray, 1825. Ann. Phil. 



PL XT. f. .;; PL XIII. f. l-.s. 



The species of this genus present great difficulties ; their small size, the usu- 

 ally imperfect condition of their preservation, the great variation in the shape 

 of the test, and the differences due to growth, make it extremely difficult to 

 eliminate the special conditions of the specimens from the specific differences; 

 as far as I can judge from the material at my command, many of the spe- 

 cies have been based upon totally inadequate characters. The specimens 



