88 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



In many species of Heterometra, in C rasped omef-ra acuticirra, and in Stephano- 

 metra tenuipinna the adults are often exceedingly variable in regard to the disposi- 

 tion of their division series beyond the first ; whereas one or more of the postradial 

 series may divide as many as four times, others may divide only once, so that, while 

 one or two radials may support from 4 to 8 or even 10 arms, the others may bear 

 no more than 2. I have endeavored to trace out the radials in which this excess 

 of vegetative power is most developed, and for this purpose have gathered data 

 from scores of specimens; but an examination of the data taken from endocyclic 

 species shows that excess of vegetative power may be displayed by any one of the 

 radials indiscriminately, though there is some indication that if one postradial 

 series divides an abnormal number of times its fellow is likely to be similarly 

 modified. Bateson's specimen of Antedon bifida with palmate arms is an interest- 

 ing example of this. In Comanthus parvicirra P. H. Carpenter has found that when 

 the arm division is unequal it is usually carried farther on the so-called posterior 

 radii, C, D, and E, than on the anterior radii, A and B ; and this appears to be a 

 more or less general rule throughout the Comasteridae. 



In many species of the genera Craspedometra, Heterometra, Thalassometra, 

 Perissometra, Pachylometra, and Crinometra, in Zygometra comata and Stylometra 

 spinifera, and more rarely and irregularly in certain species of Comanthus and 

 Capillaster, there is ordinarily a third division series developed on the inner branch 

 of each of the second division series, the counterpart of which is absent from the 

 outer (fig. 226, p. 180). Excepting only in Stylometra spinifera (fig. 219, p. 166) 

 this condition is only found in species which have the second division series con- 

 sisting of four ossicles, and the added division series is always of two ossicles. In 

 species in which this arrangement is the rule there are occasionally developed, ex- 

 cepting in Stylometra spinifera, external third division series, these usually con- 

 sisting of four ossicles like the second division series instead of being composed of 

 two like the internal. In the species of the genus Himerometra (fig. 123, p. 79), 

 which have very numerous arms, but which belong to a family in which the ma- 

 jority of the species typically have 30 arms as a result of each postradial series 

 dividing three times internally and twice externally, this peculiar arrangement has 

 become fixed. All of the third division series are always present, but the two 

 internal are almost invariably 2, the two external always 4 (3+4). There are com- 

 monly one or two division series present beyond the third, and it is interesting to 

 note that, in spite of the great number of arms, the family character shows itself in 

 the almost invariable occurrence of one more division series on the innermost 

 branch from each of the second division series than is found on any of the other 

 branches. The many-armed species of Zygometra (fig. 136, p. 79) hold the same 

 relation to Z. comata (fig. 143, p. 83) that Himerometra does to Craspedometra and 

 Heterometra, although usually it is not quite so easily seen; but it is curious that 

 nothing of the kind is observed in the closely allied Catoptometra. 



In Comatella (figs. 154, 156, p. 83). Cenometra (fig. 122, p. 79), Cyllometra, 

 Ptilometra (figs. 165, 204, p. 86), Pterometra (figs. 203, 208, pp. 137, 146), Astero- 

 metra, Stephanometra (figs. 125, 130, p. 79), Pontiometra, Dlc.hrometra, Lampro- 

 metra, Mariametra, Parametra, and <~! osndometra (fig. 214, p. 157). and in several 



