MONOGRAPH OF THE EXISTING CKINOIDS. 147 



metra the proximal pinnules are comparable to those of such species of Stephano- 

 metra as S. echinus or S. tenuipinna, though they are proportionately somewhat 

 longer and stouter. In Oligometra serripinna (fig. 315, p. 227) and in O. carpen- 

 teri the oral pinnules are strictly comparable to those of Heterometra crenulata, 

 and the segments of the second or second and third pairs have the same broad 

 processes on their prismatic ridges. In Oligometra japonica and in 0. caledonice 

 the lower pinnules are comparable to those of Amphimetra spectabilis or A. dis- 

 coidea (fig. 309, p. 223). Cennmetra (figs. 274, 278, p. 213) has essentially the same 

 proximal pinnule structure as Stephanometra monacantha (fig. 310, p. 223), but 

 P_ is usually much stouter and more as in Himerometra. In the species of the 

 genus Colobometra we find a close parallel to the species of the genus Stephano- 

 metra (see figs. 273, p. 207, and 325, p. 227). Most of the species have P 1 delicate, 

 many jointed and flexible, and from one to six of the following pinnules on either 

 side greatly enlarged, stiffened and spine-like, composed of segments with ex- 

 ceedingly spinous distal ends. Except for this last feature, characteristic of 

 the Colobometridse, these species are comparable to the large species of Stephano- 

 metra, while those with fewer enlarged pinnules are comparable to S. spicata, 

 S. monacantha, or S. indica. One species, C. diadema (fig. 325, p. 227), has P, 

 of the same character as P,, thus being similar to Stephanometra tenuipinna or to 

 S. echinus. But all the species of the genus Colobometra are peculiar in lacking 

 P , though this pinnule commonly reappears on regenerated arms. The oral 

 pinnules of Cyllometra, Decametra, and Prometra may best be compared with 

 those of the species of Lamprometra (fig. 312, p. 223) or Dichrometra (fig. 313, p. 

 223) from which they differ only in having a greater or lesser development of spines 

 on the distal borders of their component segments. In some forms, as in Deca- 

 metra Khuleri, P z is only slightly enlarged, while in others, as in Cyllometra manca 

 or C. (dbopurpurea, 1\ and also P 3 are very considerably modified. 



In the Tropiometridse (figs. 279, p. 213. and 308, p. 223) the oral pinnules differ 

 but very little in size or in character from those succeeding, which in this family 

 are much longer than usual. 



In the Calometridae (figs. 311, p. 223, and 314, 320 p. 227) the proximal pin- 

 nules resemble those of certain species of Colobometra most nearly, but Pj is much 

 more delicate and is composed of numerous very small rounded segments, and the 

 following pinnules, which may or may not be elongated, are sharply prismatic. 

 The first two segments of the earlier pinnules, especially of the first, are flattened 

 and greatly enlarged with broad dorsal processes, this modification, universal 

 throughout the family, not being found carried to such an extreme elsewhere. 



There are two types of differentiation of the oral pinnules in the Thalasso- 

 metridse. In the genera Ptilometra (figs. 280, p. 213, and 316, p. 227), Pterometra, 

 and Asterometra (fig. 285, p. 215), in which all the pinnules ai - e stiff and spine- 

 like, and the arm bases are so closely crowded against each other that there is no 

 need for any special adaptation of the proximal for protective or for tactile pur- 

 poses, P! is similar to the succeeding pinnules, but much smaller, and P, is usually 

 also smaller than P 3 . We see here indications of the course possibly followed in 



