MONOGRAPH OF THE EXISTING CKINOIDS. 105 



flange, which assists in supporting the visceral mass and which is repeated 

 on all the ossicles of the division series; the species of Pcecilometra (figs. 132, 

 p. 79, and 229, p. 186), in which the first and second brachials bear a broad dor- 

 solateral process, which is reduplicated on all the elements of the division series; 

 Oceanometra gigantea (figs. 145, p. 83, and 220, p. 168), in which the second 

 brachial (but not the first) bears a high median keel, which is repeated on the 

 outer elements of all the pairs in the division series ; many species of Mariametra^ 

 Parametra, Lissometra (fig. 216, p. 161), and Stiremetra, and certain species of 

 Asterometra (figs. 206, 207, pp. 143, 145), Cosmiometra (fig. 213, p. 155), and Tha- 

 lassometra (fig. 224, p. 177), in which the first two brachials and the elements of 

 the division series are conspicuously carinate; many species of Thalassometra 

 (fig. 223, p. 175), Stylometra (fig. 219, p. 166), and Sarametra, in which both 

 are covered with long spines ; certain species of Mariametra (fig. 684, p. 338), Crino- 

 metra (figs. 678-683, p. 338), GlyptoTnetra, Calyptometra (figs. 676, 677, p. 338), and 

 Perissometra (fig. 658, p. 329; part 1, fig. 100, p. 162), in which both bear a charac- 

 teristic tubercular ornamentation; and in many other less conspicuous ways in 

 other types. 



There can therefore be no doubt whatever that the division series of two 

 ossicles, no matter how many of them there may be, are strictly homologous 

 with the first two brachials of the free undivided arm and represent redupli- 

 cations of that pair of brachials interpolated between it and the radials. 



The comatnlids, in which the division series are invariably of two ossicles, 

 which are simple reduplications of the first brachial pair, include the majority 

 of all the known forms. All 10-armed species, except those in the genus 

 Thaumatocrinus, fall in this category, as well as all the multibrachiate species 

 in the Stephanometridse, Mariametridse, Ptilometrinae, and Perometrinse, and many 

 of those in the Zygometridse, Colobometridse, Calometridae, Thalassometrinse, and 

 Charitometridse. Promachocrinus also belongs here. 



Eudiocrinus and Dintacrinus. 



In Eudiod-inus (figs. 127, p. 79; 189, p. 109; 190, p. Ill; 191, p. 112, and part 1, 

 figs. 83, p. 136, and 84, p. 137) the arms are undivided, but both the first and 

 second pairs of brachials present the same features. The second pair is followed 

 by a syzygial pair, and is easily recognizable as homologous with the first pair 

 of brachials in the free undivided arms of other types. 



It is therefore clear that the arm structure of Eiidiocrinus is strictly com- 

 parable with that of the 10-armed species in which the first pair of brachials 

 is preceded by a IBr series, differing only in the circumstance that in Eudiocrinus 

 the outer element of the IBr series is not axillary and therefore bears a single 

 undivided arm plus a pinnule instead of a pair of arms. 



The distal element of each pair of ossicles united by a nonmuscular articu- 

 lation always bears two processes on its distal border, an arm and a pinnule (as 

 in the case of the first brachial pair), two exactly similar arms (as in the case 



