MONOGRAPH or THE EXISTING CBINOIDS. 



145 



specialized and has become very slender, delicate, and flexible, with numerous seg- 

 ments, the second, and usually also one or two additional pairs, has become greatly 

 enlarged, swollen, and stiffened, either flagellate distally or ending in a sharp spine. 

 These enlarged and stiffened pinnules point diagonally upward and form a rigid 

 and more or less spinous pro- 

 tective covering over the disk, 

 beneath which is the network 

 formed by the slender tactile 

 pinnules. 



This arrangement reaches 

 its greatest perfection in the 

 genus Cenoinetra (figs. 274, 278, 

 p. 213) and especially in such 

 species of Stephanovietra as S. 

 monacantha (fig. 310, p. 223) or 

 S. spicata. The same condition 

 is found in the species of 

 Amphimetra (fig. 309, p. 223), 

 Heterometra (figs. 268, 269, 

 p. 207), Craspedometra, Maria- 

 metra, Dichrometra (fig. 313, 

 p. 223), Liparoinetra, Lampro- 

 metra (fig. 312, p. 223), Cyllo- 

 metra, Oligometra (fig. 315, p. 

 227), and Decmnetra, though in 

 these genera the pinnules of the 

 second and following pairs 

 have delicate and flagellate in- 

 stead of sharply pointed tips. 



The extreme of the develop- 

 ment of the oral pinnules in the 

 direction of protective organs 

 is found in Hvmerometra (figs. 

 270-272, p. 207, and 326, p. 227), 

 in such species of Stephano- 

 metra as S. echinus (fig. 273, 

 p. 207, S. tenuipinna, and S. 

 oxyacajitha, in Analeidometra, 

 Oligom^trides, and Austro- 

 meira (fig. 324, p. 227), and 

 in Coloiometra diadema (fig. 

 325, p. 227). In these forms the first pair of pinnules is of the same stiffened and 

 spine-like nature as the following, and there are no tactile pinnules at all. 



On the other hand, some species, as Liparometra articulata and Lamprometra 

 gyges (fig. 312, p. 223), have the pinnules of the second and third pairs so slender 

 that, though somewhat stiffened, they are scarcely more than tactile organs. 



Fig. 207. — Latekal view of specimen 



HIUirlCA. 



ASTKBOMETUA 



