SUB-CLASS ii i-:r !:< 'in NOI DEA ci DAHOI DA 223 



Sub-Class II. EUECHINOIDEA. Bronn. 



Test composed of two vertical rows of plates in all of the ambulacra and inter- 

 Periproct either within the dor so-central system or in the posterior infer- 

 ambulacrum at a variable distance beyond. Peristome actinal, rarely anterior. 

 Jaws present or /*/. Permian to Recent. 



The older division into tin- tw.. ..nln-s of Desor, 7,v,///A/,-.x ami I < rcgulares ( = Erulocyclica 

 and Exocy/i'<-'i, Wright), with tln-ir further division into two sub-orders each (HolostomaUi and 

 Ghjphostomata of tlii- riidnrv.-lii-, and Gnatlwstomata and Atelostomata of the exocyclic orders), 

 is now superseded by the erection of five independent orders, as follows -.Cidaroida, Diadema- 

 toida, Hoi, ,-hiiu)ida, Clypeastroida, and Spatangoida. Of these the first two correspond to the 

 Rcgulares, and the remainder to the Irregulares. 1 



Order 1. CIDAROIDA. Duncan. 



" Euechinoidea with an actinal, central peristome and an abactinal periproct, 

 situated within the dorso-central system ; with internal branchiae only, and having 

 jiui-x and more or less vertically placed teeth, and a discontinuous perignathic girdle; 

 the interambulacral as well as the ambulacral plates continued beyond the peristome to 

 the true mouth. Spheridia absent " (Duncan). 



Family 1. Cidaridae. Wright. 



Test spheroidal ; the ambulacra narrow, composed of very numerous low plates, 

 which are usually primaries, rarely compound, each with a pair of pores arranged in 

 single or rarely in double series ; interporiferous areas with large and small granules 

 only. Interambulacra broad, composed of few plates, most with a large primary 

 scrobiculate tubercle, secondaries and granules. Apical system large, with five basal 

 and five radial plates, each with a perforation. Permian to Recent ; maximum in 

 Jura and Cretaceous. 



SECTION A. AMBULACRAL PAIRS OF PORES UNISERIAL. 



Cidaris, Klein (Figs. 356-358). Amb undulating or nearly straight, the 

 pores variable in their distance, and united by a groove or not. I Amb coronal 

 plates five to eleven in each column. Apical system large. Primary spines 

 very variable, even in the same species. Permian to Recent ; chiefly Jurassic 

 and Cretaceous. 



Of this genus more than 200 species have been described. These are grouped into seven or 

 eight artificial divisions, which are regarded by some as of sub-generic, or even generic import- 

 ance. The groups may be briefly noticed as follows : 



1 [The progress of the zoology and morphology of the recent Echinoidea during the last couple 

 of decades has been such as to necessitate numerous changes in the older terminology and classifi- 

 cation. The framing of an improved system, based \ipon the new grounds and expressive of the 

 modern views entertained in regard to taxonomic relationships, was the last undertaking of the late 

 Professor P. Martin Duncan. His essay on the " Revision of the Genera and Great Groups of the 

 Echinoidea," published by the Linnean Society, has been of the greatest service in extending the 

 descriptions of numerous fossil genera in the present chapter. Following the example of Lang and 

 others, Professor Duncan's classification has been adopted almost entirely. A word of special 

 acknowledgment is also due to Mr. W. Percy Sladen, for his advice and generous assistance in 

 editing this portion of the Echinodermata. TRANS.] 



