270 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



tlitm to subordinate tliem by a trinomial designation. The study of this collection 

 of Ilenricia has strongly suggested tlie possibihty that all the species of tlie genus 

 are connected by intergrades, not serially, but by numerous, often anastomosing, 

 lines. The possibilities are somewhat indicated by tlie puzzling interrelationships 

 of tlio North Pacific forms. 



If the number of sjjccies and races recognized seems large, it should be noted that 

 there are probably still more awaiting a name. Three problematical forms were 

 united with sanguinolenta, because the evidence of their distinctness was not suffi- 

 cient or because they seemed scarcely more than extremes of individual variation 

 ({)ossibly mutants or hybrid offspring); several local varieties or variant fonna? 

 of leviuscuh and multispina are unnamed; H. asthenactis is divisible into shghtly 

 differentiated northern and southern races, which seem too insecure to name at 

 present; and H. clarki is possibly composed of two very closely related species. It 

 may be added that the course followed was the best according to oiu- lights. The 

 difficulties which each species presented are noted under that species. 



Perhaps the sum of tliis rather lengthened apology for what follows is tliis : That a 

 system of nomenclature perfected for a rather limited set of animals (the higher 

 vertebrates) may not so well meet the requirements of a different class of creatures 

 wliich have evolved under very different conditions, and have been subjected to 

 possibly fewer, perhaps more numerous modifying factors. If this sj^stem of 

 nomenclature, therefore, is not rigorously adhered to, but is just a trifle altered in 

 order to make it less obviously the awkward instrument that it is, no serious 

 critcism should follow. 



Three species of Henricia have been described from the region between San Diego, 

 Cahfornia, and the equator. 77. minuta'^ (Bell), H. gracilis'' (Ludwig), 77. nana' 

 (Ludwig). 



The first is from Ecuador and probably a young specimen; nana is from the 

 Galapagos, 53 fathoms, and gracilis from ofl' the Tres Marias Islands, Mexico, and 

 from near Chatham, Galapagos, 146 to 680 fathoms. The small size of two of these 

 makes it difficult to compare them with the northern forms, especially as the figures 

 of the entire animal are not sufficiently enlarged to render much assistance. None 

 of them fall under the second division of the appended key, in which two or more 

 spinelets are present on the furrow face of the adambulacral plates. 77. gracilis 

 resembles in the fonnation of the skeleton 77. asthenactis, but its spinulatiou is of the 

 type of 77. leviuscula dyscrita. It is apparently distinct (at least subspecifically) 

 from this form. Without specimens for comparisoia a consideration of the rela- 

 tionships would be of little value, on accovmt of the variability of the species of this 

 genus. 77. nana, however, seems to be nearest 77. asthenactis or 77. aspera. The 

 variety of 77. clarki recorded from off the Revillagigedo Islands, in the following 

 pages, is entirely distinct from the species described b}^ Ludwig, although I do not 

 feel very certain that the form will not ultimately be found to be a distinct species, 

 when more and larger specimens are obtained. 



oProc. Zool. Soc, 1882, p. 122, pi. G, fig. 3. 



bMem. Mus. Comp. Zool., vol: .'?2, 1905, p. 204, pi. 13, figs. 67, 88; pi. 30, fig. 178; pi. 31, fig. 179. 



fldem, p. 207, pi. 13, figs. G5, CO; pi. 31, fig. 180. 



