266 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



species with much shorter cirri which are stouter and composed of much shorter 

 sogiucnts, Capillastcr scniosa, C. multiradiata , Comatula purjmrea, Comaster fruii- 

 C09US, Amphimetra produda, Oxymetra finschii and Dichrometra JlageUata. 



Gravelly bottoms tend to induce a type of cirrus which is more or less inter- 

 mediate between the rocky and muddj^ bottom types, and is illustrated by the 

 cirri of the species of Promachocrinus, Heliometra, Antliometra, Florometra and 

 Solanometra. 



As a general rule species living on muddy bottoms have extremely fragile 

 cirri wliich drop off at the slightest touch; the cirri of the species living on gravel 

 bottoms are almost as delicate; but the cirri of the species which live attached 

 to inorganic masses or to the morganic rigid skeletons of marine growths, and 

 especially the cirri of the species which live attached to flexible marine growths, 

 arc very tenacious. 



On the basis of a broad average it may be stated that the littoral species have 

 the most tenacious cirri, while the cirri of the deep-water forms are the most fragile. 



Though the cirri are ordinarily employed solely as organs of prehension, they 

 arc capable of use as swmimuig organs, for the young of Iridomctra nana has been 

 observed to float through the water with motionless extended arms, propeUed by 

 the very rapid movements of the cirri. 



The Innatantes, bemg pelagic and not having developed stems, never possess 

 cirri at any stage. In the Oligophreata and in the Macroplireata, however, cirri 

 are invariably present, in the latter always throughout life, and in the former 

 usually througliout life but invariably in the young, the family Comasteridae 

 only contauiing species lacking cirri when adult, though the majority of its species 

 are provided with them. In the genus Capilhsfer alone of the nine genera of the 

 CapiUastermte a species is found which loses its cirri when adult, these organs bemg 

 very higlily developed in the other six species included in that genus; in the Com- 

 actiniinsE ComatuleJla, Comatulides and Comactinia always have strongly developed 

 cirri, but four of the nine species of Comatula have no cirri when fuUy grown, while 

 they are normally greatly reduced in number in one, and occasionally quite absent 

 in very large specimens of another, of the remaining four. In young examples of 

 these four forms which more or less normaUy lack the cirri, however, they are 

 comparatively large and stout. In both the genera of the Comasterinse the cirri 

 are frequently absent, either as a specific character or through individual A-ariation, 

 and in some of the species they appear to be lost at a very early age. All grada- 

 tions are observable between such fonus as Comaster typica and Comantheria pohjc- 

 nemis in which the centrodorsal is typically exccedmgly reduced and sharply 

 stellate, countereunk to or even below the level of the radijils, with never the 

 slightest trace of cirr'', and such forms as Comaster multihrachiata and Comanthus 

 hennetti in which the cirri are extraordinarily large, stout, numerous, and well 

 developed; some species, like ComantJms annulata, usually possessing cirri but 

 occasionally being found without them; others, like Comanthina schlegelii or Comaster 

 belli, usually lacking cirri but sometunes occurring with from one or two to as many 

 as twenty, wliich are largo and show no trace whatever of degeneration, still 

 remaining. 



