110 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



liable for systematic purposes than the IIBr series, as is well illustrated in the 

 genera Nemaster, Capillaster, Coviaster, Comanthina, C omantheria, Coirvanthus, 

 Himerometi'a, and Heterometra. 



In none of the comatulids are the IBr series, the oldest and presumably the 

 most primitive of the division series, of more than two ossicles normally, but two 

 cases have been reported where they were 4(3+4). One of these was in a specimen 

 of Heterometra quinduplicava ('■'Antedon aneeps'^) recorded by Carpenter, the 

 other in a specimen of Comanthus parvicirra recorded by Hartlaub. I have per- 

 sonally verified both of these observations on the original specimens. 



In many of the multibrachiate species of the Comasteridag it not infrequently 

 happens that division series of six or even of eight ossicles occur in which the two 

 outermost are united by syzygy. Such aberrant division series always consist of 

 a series of paired elements, of which the distal invariably bears a pinnule, and 

 there is never any difficulty in homologizing them with division series of the 

 usual type. 



Systematic distnhvtion of the division aeties of HS + i). 



Whereas all comatulids excepting the species of Tfiaumafocrinus, Pentametro- 

 crinus, and Atopocrinus have at least one division series of 2, the division series of 

 4(3+4) are restricted in their occurrence entirely to the Oligophreata, where, how- 

 ever, they are found more or less commonly in a considerable number of genera. 



In the Comasteridse IIBr series of 4(3+4) are found in Capillaster, Nemaster, 

 Comaster, Comanthina, Comantheria, and Com,anthus; in the Zygometridae in all 

 but one of the species of Zygometra, and in all but one of the sjiecies of Catopto- 

 m,etra; in the Himerometridse in all the species of all the genera except Amphi- 

 metra; in the Colobometridse in Petasometra onlj^; in the Calometridae in Oreo- 

 Tnetra only; in the Thalassometridfe in Oceanometra, Crotalom,etra, and a few 

 species of Thalassometra; and in the Charitometridae in Crossometra, Perissometra, 

 Pachylometra, Glyptometra, and in most of the species of Crlnom,etra. 



In the Macrophreata there is a record of an ll-armed specimen of Antedon 

 hiiida in which the single IIBr series was 4(3+4). 



Capillaster and 'Semaster. 



In the species of Capillaster (figs. 158, p. 83; 1022, pi. 9; 1026, pi. 10; 180, 

 p. 92; and 181, p. 94) and N em-aster (fig. 182, p. 96) the IBr series are 2 and the 

 IIBr series 4(3+4), exceptionally 2; but the following series are always 3(2+3), 

 while on the free undivided arms there is only a single brachial preceding the first 

 syzygial pair. 



It is evident that here the first ossicle of the first brachial pair has been 

 suppressed, and with its suppression has gone the suppression of its counterparts 

 in the third and following division series. 



In Capillaster and Nemmter the arms arising from the IBr axillaries always 

 have both elements of the first brachial pair present, and also the division series 

 arising from the same axillaries are always 4(3+4) or 2, never 3(2+3) ; but in 

 both arms and division series arising from the IIBr and subsequent axillaries the 



