236 



ECHINODERMATA ECHINOIDEA 



SUB-BRANCH III 



Pliocene ; Sicily 



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. 



Sismondia, Desor. Test sub-pentagonal or ovoid, 

 depressed, inflated at the margin. Petaloid parts of 

 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 

 FlG- 3SO very few, continued wide apart to the margin, non- 



siibgidbosa, Goidf. conjugated. Peristome and periproct small, sunken,. 

 Mae " close to g etner - u PP er Cretaceous and Recent. 

 Euna, 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 infra - marginal. Internal structure with 

 needles, pillars, and other processes extending 

 from floor to roof, especially near the edge of the 

 test ; sometimes these are 

 fused to form concentric 

 partitions, and the ambu- 

 lacra may also be protected 

 by an inner wall. Tertiary 

 and Recent. 



FIG. 381. 



Clypeaster Aegypticus, Mich. Pliocene ; Gizeh, near Cairo. Fragment 

 howing internal calcareous deposits, aw, Auricles. 



ter, Lam. (Figs. 

 381,382). Actinal surface 

 flat, with the peristome 

 suddenly deeply sunken; 

 edge thin, undulating in 

 contour, with or without 

 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. 



This genus includes 3ome 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- 



