300 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



always of the second type, though they are peculiar in having short segments, par- 

 ticularly in tholattcr. In the genus Antedon the four east Atlantic species (A. petasiis, 

 A. bifida, A. moroccarm and A. hupferi) have cirri of the fu-st type combined with short 

 stout arms (figs. 103, p. 165, and 104, p. 167), as is also the case in the American 

 species, A. dubenii; ■w\\i\g those of A. mediterranea and A. adriatica, confined to the 

 Mediterranean Sea, are of the second type, correlated with elongated and slender 

 arms (figs. 105, p. 169, and 106, p. 171). Compsometraincommoda (fig. 107, p. 173) 

 also possesses cirri of the first type combined with comparatively stout arms, wlfile 

 its near relative, C. loveni (fig. 108, p. 174) has cirri only of the second type and 

 slender arms. I am not sure that the exceedingly long and stout cirri of Ilaihrometra 

 prolixa, by wliich that species is at once differentiated from all the others of the 

 genus, and which are more or less strongly differentiated as a class from the smaller 

 cirri in the same species, should not be considered as belonging to the first type. 



The cirri of the numerous species belonging to the Ilimcrometridie (figs. 335 

 p. 283, 336-339, p. 285), the Step hanometridse (fig. 340, p. 287), and the Mariametridse, 

 (figs. 341-344, p. 287), show great variation. Sometimes the charitometrid type may 

 be made out, sometimes the thalassometrid, and again the cirri appear to be of 

 the typo indicating a slow and progressive mcrcase in length as seen in the 

 Macrophreata. As a rule the dorsal spines when developed are very long and 

 quite distmctive, though exactly the same tj^pe occurs in Zygometra (figs. 332, 333, 

 p. 283) ; they are often unusually long, and are slender, very sharp, subterminal to 

 ahnost median (distally), and make a very large angle with the longitudinal axis 

 of tlic segments, especially in the outer part of the cirri. This condition is per- 

 ha])s seen most perfected in Stephanometra echinus and in S. tenuipinna. Many 

 species belonging to these families have cirri which, though without dorsal spines, 

 are very sharply carinate dorsally in the outer part. This tendency to an excessive 

 dorsal com])ression is probably correlated with the length and slenderness of the 

 dorsal spines when they are developed. Running through the Himerometridae (cul- 

 minating in Craspedometra) (fig. 85, p. 139) we notice a tendency toward a distal 

 tapering of the cirri, correlated with a proportionate increase in the length of the 

 distal segments and a progressive suppression of dorsal processes or carina tion; 

 the cirri of Craspedometra (fig. 85, p. 139) are very long with numerous segments, 

 smooth, very stout basally, but tapering to a slender sharp pointed tip, the length 

 of the segments increasing gradually from the base outward. 



The cirri of the Colobometridse (figs. 345-348, p. 289, 349-352, p. 291, and 353- 

 355, p. 293) are pecuhar in being especially broad, and, though narrower distally, 

 they do not attain to any great degree of lateral compression. In Cenometra (fig. 

 345, p. 289) they are both broad and stout, composed of very short subequal segments 

 wliich have a more or less marked dorsal median longitudinal furrow, and bear on 

 each segment two dorsal spines, one on each side of the furrow. The cirri of 

 Oligometra (fig. 352, p. 291) are essentiaUj' the same as those of Cenometra; but the 

 very small size of the animals has endowed them with certain more or less primi- 

 tive characters; the component segments, wliich are subequal, are usually nearly 

 or quite as long as broad, and each (except a few at the base of the cirri) bears 

 dorsally an uninterrupted transveree ridge, strongly serrate along its crest which. 



