308 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



method of arm reduplication, which is unique among living comatulids, though occur- 

 ring in the pentacrinitos. The 2 outer arms on each ray first appear as buds in the 

 position of the usual Pi on the original 10 arms. These buds develop into arms 

 which reach the size of the 10 original — now inner — arms when the animal becomes 

 adult. 



In Comatula pectinata, which may have as many as 17 arms, the additional arms 

 arise in the usual way by the breaking off of the original arm at the articula- 

 tion between the first 2 brachials and the development of an axillary bearing 2 arms 

 on the stump or exposed articular surface of the first brachial. 



In arms arising from a IIBr axillary the first syzygy is between brachials 1 + 2, 

 and on the outer arm this is immediately followed by another syzygy between bra- 

 chials 3+4. The arm division in multibrachiate species or individuals of Comatula 

 is therefore of the type characteristic of ComateUa and its allies. 



Most of the 10-armed species of Comatula are remarkable for the great diversity 

 of their arm structure. The arms may be slender or stout, short, or very greatly 

 elongated. Often the posterior arms are short and broad, the anterior very long 

 and attenuated. In some cases as few as 4 of the 10 arms may bear ambulacral 

 grooves. 



KET TO THE SUBGENERA OF COMATULA 



o'. Arms 20 (rarely more) in number; no cirri; in young individuals with cirri the outer arm on 

 each IIBr series is smaller and shorter than the inner (Aru Islands and northern Australia 

 south to Baudin Island, Western Australia, and Port Molle, Queensland; 0-69.4 meters) 

 Vslidia, p. 308. 



a*. Arms less than 20, usually 10, in number; the 2 arms from the same axillary always of the 

 same length; cirri usually, though not always, present (Ceylon and the Gulf of Martaban 

 to AustraUa, south to between Fremantle and Geraldton, Western Australia, and Sandon 

 Bluffs, New South Wales, northward to Luzon, the China Sea, and Hong Kong, and cast- 

 ward possibly to the Society Islands; 0-109 meters) Comatula, p. 320. 



Subgenus Validia A. H. Clark 



Comatula (part) Lamarck, Hist. nat. des animaux sans vertebres, vol. 2, 1816, p. 534, and follow- 

 ing authors. 



Alecto (part) J. Muller, Monatsber. d. k. preuss. Akad. d. Wiss., 1841, p. 184. 



Comatula (Aclinometra) (part) J. Muller, Abhandl. d. k. preuss. Akad. d. Wiss., 1847, 1849, p. 256. 



Actinometra (part) P. H. Carpenter, Proc. Roy. Soc, vol. 28, 1879, p. 390, and following authors. 



Actynometra (part) Filhol, La vie au fond des mers, 1885, p. 214. 



Validia A. H. Clark, Vidensk. Medd. fra den naturhist. Forcning i K0benhavn, 1909, p. 142 

 (characters; genotype Comatula rotalaria Lamarck, 1816) ; Unstalked Crinoids of the Siboga 

 Exped., 1918, p. 24 (in key to the genera of Comactiniinae; range). 



Comatula (Validia) A. H. Clark, Unstalked Crinoids of the Siboga Exped., 1918, pp. 6, 25. 



Diagnosis. — A subgenus of Comatula including species in which the arms are 

 usually 20 (from 18 to 27) in number. There are no cirri in the adult stage, the 

 centrodorsal being reduced to a stellate plate sunken within the radial circlet. 



The young possess 10 arms and cirri. The additional 10 arms develop from a 

 bud which appears in the place of P, and grows into an outer arm. In young indi- 

 viduals, therefore, the outer arms of each IIBr series are smaller and shorter than 

 the inner, not reaching the size of the inner arms until the animal is well grown and 

 has lost all, or nearly all, the cirri. 



