226 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



ters as by the fact that they do not fall in the genera Craspedometra, Himerometra, 

 Amphimetra, or Homalometra. 



The genus Heterometra is divisible into five fairly well marked groups, which 

 might possibly be considered as of subgeneric value. But with our present meager 

 knowledge of most of the species it is quite inadvisable to subdivide it. 



In the first group the enlarged lower pinnules are comparatively slender and 

 are entirely smooth, with no carination of the basal segments and no modification 

 of the distal ends of the outer segments. The two species in this group, H. savignii 

 and H. nematodon, appear not to be very closely related to each other. 



Another group in which the cirri are smooth, the distal segments being without 

 dorsal processes although they may be more or less strongly carinate, and the en- 

 larged lower pinnules are usually smooth though in large individuals the basal segments 

 may be slightly carinate, is represented by H. quinduplicava only. Though in the 

 character of the enlarged lower pinnules H. quinduplicava is intermediate between 

 the species with these pinnules smooth and the species with these pinnules carinate 

 basally, it is quite unique hi the character of its cirri. 



In a third group the enlarged lower pinnules have the outer segments with their 

 distal ends armed with spines or with rounded triangular extensions of the distal 

 portions of the prismatic ridges. In H. variipinna the enlarged lower pinnules are 

 composed of cylindrical segments with spinous distal ends, while in H. crenulata the 

 lower pinnules are very strongly prismatic with the distal ends of the prismatic 

 ridges on each segment produced into conspicuous rounded triangular lateral exten- 

 sions so that the profiles of these pinnules are very strongly serrate, the teeth being 

 broadly rounded. Heterometra crenulata is exceedingly variable in every feature. 

 Individuals are not infrequent in which there are only 10 arms, though in others there 

 may be as many as 30 arms. Individuals vary from extraordinarily robust with 

 stiff and spinelike enlarged lower pinnules to very slender with slender lower pinnules 

 which become almost flagellate distally. The processes on the segments of these 

 pinnules may be broad and involve basally a large part of the segment, or they may 

 be reduced to scarcely more than an overlapping spine. The cirri may be prominently 

 spiny or practically smooth, stout, or slender and tapering. Some forms of H. cren- 

 ulata approach H. producta which may possibly turn out to be merely an extreme 

 variation of it while H. producta and H. propingua probably will be found to inter- 

 grade. Although H. crenulata and H. variipinna seem to be so very different, the 

 enlarged lower pinnules in the latter may be more or less prismatic, at least basally, 

 suggesting that the two species may be rather closely allied. 



In all the other species of Heterometra the enlarged lower pinnules are entirely 

 smooth, but their earlier segments bear more or less strongly developed and usually 

 conspicuous carinate processes on the side toward the arm tip. They are divisible 

 into two quite distinct groups. 



The first of these, or the fourth group of Heterometra as a whole, includes 11 

 species astyanax, qffinis, reynaudi, amboinae, ater, joubini, pulchra, gravieri, compta, 

 singularis, and madagascarensis. In these species the brachials, though actually 

 short, are relatively long, and are always more or less wedge-shaped with oblique 

 ends, the earlier brachials, beyond the first few, being markedly wedge-shaped and 

 in some cases almost triangular. This group is divisible into three subgroups one 



