284 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.46. 



A. H. Clark, Smiths. Misc. Coll. (Quart. Issue), vol. 52, 1908, p. 214 . .bartscM (5) 

 A. H. Clark, Proc. Biol. Soc. Washington, vol. 22, 1909, p. 7; Crinoids of the 



Indian Ocean, 1912, p. 116 bartschi (5) 



persica (6) 

 Eimerornetra pulcher A. II. Clark, Crinoids of the Indian Ocean, 1912, p. 114 



robustipinna (2) 



Eimerornetra robustipinna A. H. Clark, Smiths. Misc. Coll. (Quart. Issue), vol. 52, 



1908, p. 213; Proc. Biol. Soc. Washington, vol. 22, 1909, p. 7 .robustipinna (2) 



Eimerornetra sol A. II. Clark, Crinoids of the Indian Ocean, 1912, p. 115 sol (4) 



Eimerornetra sp. A. H. Clark, Notes from the Leyden Museum, vol. 33, 1911, p. 182; 



Crinoids of the Indian Ocean, 1912, p. 117 robustipinna (2) 



A. H. Clark, Smiths. Misc. Coll., vol. 60, 1912, No. 10, p. 18 ... .robustipinna (2) 



THE PHYLOGENETIC INTERRELATIONSHIPS OF THE SPECIES OF THE 

 GENUS HIMEROMETRA. 



Though the structure of the cirri and of the arms is in all remarkably 

 uniform, on the basis of the structure of the proximal piimules the six 

 species of the genus Eimerornetra fall into three groups of two each, 

 and these three groups appear to represent three distinct steps in 

 phylogenetical advancement. 



In the allied genera Craspedometra and Heterometra the enlarged 

 proximal pinnules are, though greatly elongated, comparatively 

 slender, and become very delicate and flagellate distally; they are 

 more or less carinate proximally, and the component segments meet 

 end to end without any overlappmg; the first pimiule (mcluding the 

 pinnules on the division series if any be present) is shorter than the 

 second, and the second is shorter than the third. 



In Himerometra persica and H. hartscJii the proximal pinnules, 

 excepting m their relative proportions, are not very different from the 

 type characteristic of Craspedometra and of Heterometra — they are 

 comparatively slender, becommg very delicate and flagellate distally, 

 are composed of smooth segments which meet evenly end to end, and 

 have retained to some extent the proximal carination. Himerometra 

 hartscJii, with its more numerous arms and cirrus segments and the 

 shorter and much less strongly carinate basal segments of its proximal 

 pinnules, is more highly differentiated from the primitive type than 

 is H. persica. 



In Himerometra sol and H. magnipinna the proximal pinnules are 

 exceedmgly stout and have lost all trace of the carination of their 

 basal segments, while the middle and outer segments have developed 

 everted and prominent distal ends; they still retain, however, the 

 flagellate tip. In H. sol the proximal pmnules appear to include a 

 greater number of segments than do those of H. magnipinna, while 

 the eversion of the distal edges of the segments is much more strongly 

 ma^'ked, and is smooth and not spinous or serrate. H. sol therefore 

 may be considered a less specialized type than H. magnipinna. 



