SUB-CLASS II EUECHINOIDEA—CIDAROIDA 225 
(c) Letocidaris, Desor. Like the preceding, but with uncrenulated tubercles. Spines large, 
smooth, cylindrical. Cretaceous to Recent. 
(d) Dorocidaris, A. Ag. Like Cidaris, but with smooth tuberctes. Recent. 
(e) Stephanocidaris, A. Ag. ‘Test thin ; apical system larger than the peristome, the plates 
feebly united, and the whole flexible. Recent. 
(f) Phyllacanthus, Brandt. Test large, swollen, and with eight to eleven [dmb plates. Amb 
pores in a broad zone, conjugated. Primary tubercles large, smooth, perforate. Recent. 
(9) Porocidaris, Desor (Fig. 361). Amb broad and straight ; pores wide apart, conjugated. 
Primary tubercles perforate and crenulate. Scrobicules transversely oval, with shallow grooves 
radiating from the periphery toward 
the centre, with or without pores at 
the outer extremity of the grooves. 
Tertiary and Recent. 
(h) Goniocidaris, Desor. Test high, 
with numerous coronal plates, and 
narrow dmb. The median sutural 
regions of both areas are sunken, form- 
ing with the horizontal sutures a zigzag, 
with pit-like depressions at the angles. 
Recent. 
Orthocidaris, Cott. Apical 
system small, pentagonal. dmb 
narrow, straight ; pairs of pores 
in simple straight series, the 
pores separated by a granule. 
IAmb very broad, numerously 
plated. Primary tubercles small, 
plain, perforate, and distant. 
Lower Cretaceous ; Europe. Ea 
Lemnocidaris, Cott. Upper Rhabdocidaris a Orbignyana, _ Desor- 
Cretaceous. Polycidaris, Quenst. Te Pe agian em Ueeieern cee 
Upper Jura. enlarged. 


SECTION B. AMBULACRAL PAIRS 
OF PoRES BISERIAL. 
Diplocidaris, Desor. Test 
large, spheroidal. Amb narrow, 
straight ; poriferous interporifer- 
ous zones of equal width. Pairs 
of pores very numerous, close, 
alternating more or less. LAmb 
broad, with seven to eight plates 
ineachcolumn. Primary tubercles 
large, perforate, scrobiculate. 
Upper Jura ; Europe. pkey 
Tetracidaris, Cott. (Fig. 362) meee BESSA ty | 
Remarkable in having four Porocidaris Schmiedeli, Goldf. Nummu- homtia Mee 
coronal plates in each TAmb at Pano De eetone Mokkatam, near Cairo. Ie Jura. 
: aa Ta 4 Ve tam y. plate and spine. Spine, 1/;. 
the ambitus, but diminishing to 
two at the apex. [It should be noticed, however, that A. Agassiz has observed 
a somewhat similar division in the /4mb plates of the recent genus Astropyga. | 
Amb straight, moderately broad. Poriferous zones depressed, pairs incom- 
pletely biserial ; interporiferous areas narrow, granular, with a row of plain 
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