236 ECHINODERMATA—ECHINOIDEA SUB-BRANCH III 
far apart. Peristome central, pentagonal, with small jaws. Periproct  be- 
tween the peristome and posterior edge of the test. 
Cretaceous to Recent. 
Sub-genus.—Scutellina, Ag. Periproct small, marginal, or 
more or less supra- or infra-marginal. Tertiary. 

aes aie Sismondia, Desor. Test sub-pentagonal or ovoid, 
Echinocyamus placentus, 
Goldf. sp. (E. siculus, Ag.) Gepressed, inflated at the margin. Petaloid parts of 
EOC e 5 Pie al the Amb usually long, more or less open; pairs of 
pores not continued actinally. Tubercles minute. 
Eocene and Miocene. 
Fibularia, Lam. (Fig. 380). Test thin, ovoid, tumid 
dorsally and at the side. Amb short; pairs of pores 
Fic. 380. very few, continued wide apart to the margin, non- 
Fibularia subglobosa, Golat, Conjugated. Peristome and periproct small, sunken, 
Stich ay es? MAe close together. Upper Cretaceous and Recent. 
Runa, Ag. Tertiary ; Europe. 

Family 2. Clypeastridae. Agassiz. 
Test small to very large, depressed, flat, or high. Petaloid parts of the ambulacra 
highly developed, usually unequal ; the actinal furrows straight. Interambulacra 
actinally discontinuous ; one peristomial and two apical plates in each. Peri- 
gnathic processes tall, narrow, two on each ambu- 
lacrum, fitting in below the large jaws. Peristome 
central, pentagonal ; periproct small, marginal 
or imfra-marginal. Internal structure with 
needles, pillars, and other processes eatending 
from floor to roof, especially near the edge of the 
test ; sometimes these are 
fused to form concentric ; ‘ 
partitions, and the ambu- t ex Da i 
lacra may also be protected 
by an inner wall. ‘Tertiary 
and Recent. 



Clypeaster, Lam. (Figs. 
381,382). Actinal surface 
flat, with the peristome 
suddenly deeply sunken ; 
edge thin, undulating in wae i ; ; Joa 
: . Clypeaster Aegypticus, Mich. Pliocene; Gizeh, near Cairo, Fragment 
contour, with or without showing internal calcareous deposits. au, Auricles. 
re-entering angles. Petals 
long, broad, tumid; pores wide apart, unequal, conjugated. Periproct near 
or at the edge. Internal structure not forming a double wall covering the 
Amb. ‘Tertiary and Recent. 
Fic. 381. 
This genus includes some of the largest Sea-urchins known. Recent species are littoral, 
or shallow water inhabitants. 
Diplothecanthus, Duncan (Echinanthus, Breyn. p.p.) Margin and actinal 
surface tumid, but hollow from the margin to a deep central peristome.  In- 
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