3 02 



THE ECH1NOIDEA 



Hall, Devonian and Lower Carboniferous ; Koninckocidaris, Dollo & 

 Buisseret, and Perischodomus, M'Coy, both Carboniferous. The main 

 character of the family is that none of the interambulacral plates occur 

 detached from the test on the peristomial membrane (Fig. XV.). 1 



FAMILY 2. ARCHAEOCIDARIDAE. Cidaroida with ambulacral pore- 

 pairs in a single series. Interambulacral plates in more than two vertical 

 rows. Test slightly flexible, owing to slight imbrication of plates. 

 Peristome large, several rows of the interambulacral plates as well as of 

 the ambulacral passing on to the peristomial membrane. The main char- 

 acter of this family is that, while the interambulacral plates remain in 

 more than two series and somewhat imbricated, in both of which 

 features it agrees with- the Lepidocentridae, it has acquired the peristomial 

 characters of the true Cidaridae. Genera Archaeocidaris, M'Coy (Fig. 



Fio. XVI. 



1, Palceechiniis sphaeriwts, M'Coy; Carboniferous. 2, A plate and spine of Archaeocidaris 

 iirii, Fleni. ; Carboniferous. 3, Cidaris ylandifera, Golclf. ; Jurassic. 4, Hemicidaris intermedia, 

 Fleiu. ; Mid. Jurassic. 5, Salenia ]>etalifera, Uesni. ; Cretaceous. 6, Dysaster ringens, Ag. ; 

 Jurassic. 7, Enallaster Greenovi, Forbes ; Cretaceous. 8, Catopyffiis columbarius, Lam. ; 

 Cretaceous. 



XVI. 2), and Lepidocidaris, Meek & Worthen, both Carboniferous. In 

 the latter some of the ambulacral plates are demi-plates. Xenocidaris, 

 known from spines only, may also belong here. 



FAMILY 3. CIDARIDAE. Cidaroida with ambulacral pore-pairs uni- 

 serial and plates all primaries. Interambulacral plates in two vertical 

 series in each area. Test rigid, as the plates do not imbricate. Several 

 rows of interambulacral and ambulacral plates pass on to the peristomial 

 membrane. The family includes the living genus Cidaris, Leske, with 

 its numerous subdivisions Rhabdoridaris, Chondrocidaris, Stereocidaris, 

 Discoddaris, Tylocidaris, Typocidaris, Dorocidaris, etc. Goniocidaris, Des.; 

 Orthocidaris, Cott ; Temnocidaris, Cott ; Polycidaris, Quenst, are also 

 genera of this family. Cidaris is one of the most primitive of recent 

 Echinoids, and therefore one of the most instructive. 



(41). 



The systematic value of this character is shown in Jackson's interesting paper 



