ORDER III EUECHINOIDEA—HOLECTY POIDA. 233 
present. J4mb with two rows of primary, and four or more of secondary 
tubercles. Late Tertiary and Recent. 
Sphaerechinus, Desor. Amb straight, wide. Pairs of pores in ares or 
oblique lines of four to eight pairs, polyserial actinally. Interporiferous areas 
with two to six vertical rows of plain, imperforate primaries, and horizontal 
rows of secondary tubercles and miliaries. _L4mb 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. L4mb 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. Tvripneustes, Ag. Miocene and Recent. 
Leiopedina, Cott. (Chrysomelon, Laube). Test large, melon-shaped. dmb 
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. Ldmb 
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, 
“ KRuechinoidea with an actinal, central peristome, and the periproct situated be- 
yond the dorso-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.”—Dunean. 
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. J4mb with rather large plates, and 
many rows of tubercles. Peristome large, decagonal, with well-marked 
branchial incisions, jaws, and feeble perignathie girdle. Periproct large, 
