214 BULLETIN 82, UNITED STATES NATIONAL. MUSEUM. 



brachial pairs, together with the radials. The first type is always accompanied by 

 a strong lateral compression of the brachials, and the carination has a tendency to 

 lean anteriorly, taking the form of a more or less broad overlapping spine. The 

 second type is, on the other hand, accompanied by a considerable broadening of the 

 plates affected, and the carination is perfectly erect. 



Carination of the distal brachials does not occur unless those segments are 

 smooth dorsally; but carination of the division series and first two brachials is 

 almost invariably accompanied, as in Crinometra (figs. 678, 680, 683, p. 338), Maria- 

 metra (fig. 684, p. 338), Glyptometra, Perissomctra (fig. 658, p. 329), Cotylometra 

 (fig. 199. p. 129), Oceanometra (figs. 220-222, pp. 168-173), and Thalassometra 

 (fig. 224, p. 177), by a spinous or tubercular modification of the dorsal surface. 



In the Comasteridse a very thin, narrow, low, and inconspicuous median eleva- 

 tion which can be detected only with difficulty occurs more or less constantly on 

 the brachials of certain species of Comatula, and in Comatonia a few of the lower 

 brachials have the central portion elevated into a blunt keel with a spinous crest. 

 Except for these cases neither type of carination is ever found in the Comasteridse 

 other than as a rare variant, nor in the Zygometridse, Himerometridse, or Stephano- 

 metridae. Proximal carination occurs in all the species of Mariametra (figs. 196, 

 p. 124, 197, p. 125, and 684, p. 338), though never found in those of Dichrometra, 

 Oxymetra (fig. 195, p. 122), or Pontiometra (fig. 194, p. 120), and in Cotylometra 

 ornata (fig. 199, p. 129), though not in C. gracilicirra nor elsewhere in the Colo- 

 bometridse. In the Tropiometridse distal carination is characteristic of all the 

 smaller species of Tropiometra (fig. 173, p. 89), but is not found in the two largest. 

 It occurs in all of the species of Calometridae, in one genus of which there is also a 

 very slight proximal carination in a few of the species. 



It is in the Thalassometridae that both types attain their maximum develop- 

 ment. In the Ptilometrinae the distal carination is excessive, though usually it does 

 not occur on the lower part of the arm ; but certain species of Asterometra (those 

 allied to A. longicirra [figs. 206, 207, pp. 143, 145]) and of Pterometra (those allied 

 to Pt. trichopoda [fig. 208, p. 146]) may possess very strongly marked proximal 

 carination, this reaching its maximum in some of the species of the former (figs. 

 206, 207, pp. 143, 145), though entirely absent from others (fig. 209, p. 149, and part 

 1, fig. 94, p. 155). In Stiremetra and in Cosmiometra (figs. 213, 214, pp. 155, 157) 

 only proximal carination occurs, in the latter being only faintly evident. In 

 Stylometra (fig. 219, p. 166, and part 1, fig. 35, p. 73) only distal carination is found, 

 here, however, reaching its greatest development. In Parametra both types are 

 found, the distal, except in one species (fig. 218, p. 164), strongly marked, the 

 proximal scarcely noticeable. In Thalassometra both types are found, though 

 never in the same species. In Oceanometra gigantea (fig. 220, p. 168) the proximal 

 carination is curiously restricted to the second element of the first brachial pairs 

 and to their morphological reduplications, never occurring on any of the other seg- 

 ments. The species of Stenometra (fig. 211, p. 152) and Daidalomctra (fig. 212, p. 

 153) have all the postradial ossicles very strongly carinate. 



