ORDER m EUECHINOIDEA HOLECTYPOIDA 233 



present. I Amb with two rows of primary, and four or more of secondary 

 tulu-rclcs. Late Tertiary and Recent. 



Sphaerechinus, Desor. Amb straight, wide. Pairs of pores in arcs or 

 oblique lines of four to eight pairs, poly serial actinally. Interporiferous areas 

 with two to six vertical rows of plain, imperf orate primaries, and horizontal 

 rows of secondary tubercles and miliaries. I Amb with two to twelve vertical 

 rows of primaries. Pliocene and Recent. 



Eurypneustes, Aeolopneustes, Duncan and Sladen. Eocene ; Asia. 



Family 8. Echinidae. Wright. 



Test symmetrical ; ambulacra and interambulacra of equal width. Ambulacral 

 plates compound, with three pairs of pores, which are arranged in high or low arcs of 

 triplets. Coronal plates without pits and grooves, and their opposed surfaces plain. 

 Teeth keeled. Cretaceous to Recent. 



Echinus, Rond. Amb straight, with narrow poriferous zones ; pore pairs 

 in more or less vertical arcs of triplets. Interporiferous areas with two 

 vertical rows of small, plain, primary tubercles, with or without irregularly 

 placed secondary tubercles and primaries. lAmb with two vertical rows of 

 primaries, and few or numerous rows of secondary tubercles and miliaries. 

 Peristome small, circular ; the buccal membrane with ten buccal plates bearing 

 tentacles and small spines. Cretaceous to Recent. 



Subgenus Psammechinus, Ag. Like Echinus, but the buccal membrane with numerous 

 concentric plates, besides the ten buccal plates. Cretaceous to Recent. 



Stirechinus, Desor. Both areas with two rows of large, plain, primary 

 tubercles situated on raised keel-like projections. Pliocene ; Europe. 



Glyptechinus, de Loriol. Cretaceous. Tripneustes, Ag. Miocene and Recent. 



Leiopedina, Cott. (Chrysomelon, Laube). Test large, melon-shaped. Amb 

 long, straight, very broad. Poriferous zones broad, pairs of pores triserial, 

 and almost horizontal. Plates very numerous, low, broad, compound. 

 Tubercles small, plain, finely perforate, in two distant vertical rows. lAmb 

 broad, with two rows of tubercles similar to the ambulacral, and with inter- 

 mediate granules. Eocene. 



Hypechinus, Desor. Tertiary. Toxopneustes, A. Ag. (non Ag.) Recent. 

 Boletia, Desor. Recent. 



Order 3. HOLECTYPOIDA. Duncan. 



" Euechinoidea with an actinal, central peristome, and the periproct situated be- 

 yond the dor so-central system in the posterior interambulacrum ; with external branchiae; 

 with a pair of pores or only one pore to an ambulacral plate ; with feeble jaws and 

 vertical teeth, or without these structures ; with a variably constructed perignathic 

 girdle. Spheridia present." Duncan. 



SECTION I. Perignathic processes of the ambulacra present. 

 Holectypus, Desor (Fig. 375). Amb narrow, straight, widest at the am- 

 bitus; some of the plates compound. I Amb with rather large plates, and 

 many rows of tubercles. Peristome large, decagonal, with well -marked 

 branchial incisions, jaws, and feeble perignathic girdle. Periproct large, 



