256 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



The cirri are arranged hi more or less crowded alternating rows hi all the 

 macrophreate genera except hi those included in the subfamily Zenometrhite (figs. 

 109, p. 175, 110, p. 176, 111, p. 177, 208-216, p. 241, 228, p. 245, and 558, pi. 5), hi 

 Atopocrinus (fig. 227, p. 245), and in Atelecrinus (figs. 123, p. 192, 124, 125, p. 193, 

 218, 223, p. 243, 414, p. 319, and 573, 574, pi. 8), where they are arranged in col- 

 umns. These six genera, therefore, are at once distinguishable from all other 

 comatulid genera by a glance at the centrodorsal. Moreover, they are at once dis- 

 tinguishable among themselves; hi Atelecrinus (figs. 123, p. 192, 124, 125, p. 193, 

 218, 223, p. 243, 414, p. 319, and 573, 574, pi. 8) the cirrus sockets are bounded 

 laterally, or laterally and ventrally, by a strong horseshoe-shaped ridge, or by high 

 lateral ridges, whereas in the other genera they are mere undifferentiated pits in the 

 general surface of the centrodorsal; there are 10 or 15 very definite columns of cirrus 

 sockets, but the surface of the centrodorsal is not marked off into radial areas. 

 This is the case also hi Leptometra (figs. Ill, p. 177, and 219, p. 243) and in Adelo- 

 metra, but hi the former they are entirely separated from each other, while hi the 

 latter they are closely crowded. 



In Atopocrinus (fig. 227, p. 245) the centrodorsal is very long and sharply 

 conical and is divided into 10 narrow cirriferous areas by five high serrate inter- 

 radial and five smaller similarly serrate midradial ridges. Each cirrus socket 

 projects strongly over the proximal portion of the one just below it and possesses 

 strong fulcral ridges which are not found in the cirrus sockets of the species of 

 Zenometrinaj (figs. 109, p. 175, 110, p. 176, 111, p. 177, 208-216, p. 241, 228, p. 245, 

 and 558, pi. 5). 



In Balanometra, Zenometra (figs. 109, p. 175, 214-216, p. 241, and 558, pi. 5) and 

 PsatJiyrometra (figs. 110, p. 176, 208-213, p. 241, and 228, p. 245) the centrodorsal is 

 divided into five radial areas by strongly developed ridges, furrows, or broad bare 

 areas. In Balanometra and in the Atlantic species of Zenometra (figs. 215, 216, 

 p. 241, and 558, pi. 5) there are 10 columns of cirrus sockets, two in each radial 

 area; Balanometra has the radial areas marked off by broad furrows, and the two 

 columns of cirrus sockets in each radial area more or less widely separated, 

 whereas in the Atlantic species of Zenometra the radial areas are delimited by 

 strong ridges, and the two columns of cirrus sockets in each radial area are close 

 together. In the Pacific species of Zenometra (figs. 109, p. 175, and 214, p. 241) 

 and in Psathyrometra there are three or four columns of cirrus sockets in each 

 radial area, these radial areas being marked off by bare spaces not raised above 

 the general surface of the centrodorsal. In Zenometra triserialis the distal portion 

 of the centrodorsal is thickly covered with spines, while the three equal columns 

 of circular cirrus sockets in each radial area are closely crowded. In Psathyro- 

 metra the dorsal pole of the centrodorsal is smooth, and the cirrus sockets are 

 arranged in three or four columns in each radial area; they are usuall} 7 more or 

 less separated, and each cirrus socket is correspondingly separated from its neigh- 

 bors hi the same column. If there are three columns in each radial area, the 

 median column tends to be deficient, the outer columns converging and meeting 

 beyond it. In one species this middle column is reduced to a single socket. If the 

 columns of cirrus sockets are crowded, the sockets become dorsoventrally elongate. 



