216 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



In the Charitometridae no true carination is found, either proximal or distal. 

 In the genera Crossometra (figs. 673, 675, p. 335), Perissometra (figs. 658, p. 329, 

 and 670, p. 335, and part 1, fig. 100, p. 162), Pachylometra (figs. 671, 672, p. 335), 

 Chondrometra (part 1, fig. 99, p. 160), Chlorometra (fig. 228, p. 184), Calyptometra 

 (figs. 676, 677, p. 338), and Crinometra (figs. 678-683, p. 338, and 674, p. 335) the 

 dorsal surface of the division series and lower brachials is commonly tuberculated. 

 These tubercles may be coarse, low, and irregular as in Chondrometra robusta, 

 Perissometra lata (fig. 658, p. 329), or Crossometra investigatoris (fig. 673, p. 335), 

 or they may be small, high, and subequal in size as in Crinometra margaritacea 

 (fig. 683, p. 338). Often a generally rugose or tuberculated surface bears a median 

 line of high rounded tubercles, as in Perissometra selene (fig. 227, p. 182) or in 

 Crinometra concinna (fig. 678, p. 338), or a more or less sharp median carination 

 standing out prominently as in Glyptometra tiiberosa. In these genera the median 

 line of the division series and of the first brachial pairs is usually occupied by 

 larger tubercles than the remainder of the dorsal surface, or it may, as in Maria- 

 metra subcarinata (fig. 684, p. 338), be quite smooth, the tubercles being confined 

 to the interradial areas. In Aglaomctra eupedata (fig. 225, p. 179) each of the 

 elements of the IBr series has a single large rounded tubercle on either side. 



None of the macrophreate species possess any trace of either type of carination. 



In certain of the Macrophreata (part 1, figs. 112, p. 179, and 110, p. 176), 

 much more rarely in the Oligophreata (figs. 192, 193, 200, pp. 115, 117, 130, and part 

 1, fig. 86, p. 141), the articular fulcral ridges of the apposed joint faces are pro- 

 duced outward, forming strong and very prominent tubercles. The tubercles 

 formed at the synarthries are always larger than those formed at the oblique 

 muscular articulations, and they are more prominent as they occupy the median 

 dorsal line; these are known as synarthrial tubercles. The tubercles formed 

 at the oblique muscular articulations only occur between the more or less oblong 

 brachials at the base of the arm (fig. 233, p. 193, and part 1, fig. 121, p. 189) ; 

 they are from four to eight in number and rapidly diminish in size distally. 

 Their prominence is not necessarily correlated with that of the synarthrial tubercles. 



Synarthrial tubercles are rather strongly developed in all of the larger 

 Antedonidae; they are very prominent in the Zenometrinse, especially in Psathyro- 

 metra (part 1, fig. 110, p. 176), and reach their maximum in the genus Perometra 

 (part 1, fig. 112, p. 179) and in Neometra diana (fig. 200, p. 130). Curiously 

 enough, they are equally large in the oligophreate Amphimetra ensifer (part 1, 

 fig. 86, p. 141) and well developed in A. discoidea, though obsolete or quite non- 

 existent in all the other oligophreate forms, as well as in the Atelecrinidse and 

 in the Pentametrocrinidae. 



When the articular tubercles between the proximal arm ossicles are developed 

 the arm base is said to be tubercular. As the tubercles alternate with each other 

 on either side of the arm the effect is very characteristic (fig. 233, p. 193, and 

 part 1, fig. 121, p. 189). 



Such tubercular arm bases are characteristic especially of the species of 

 Heliometrinse and Pentametrocrinidse among the macrophreate forms, and of 



