A MONOGRAPH OF THE EXISTING CRINOIDS 71 



j'. Pi similar to Pj, but shorter; cirri exceedingly long (Japan to Tasmania and 

 southern Australia, westward to the Bay of Bengal; sublittoral, in south Aus- 

 tralia also littoral) PtUometrinae (pt. 4). 



if. Pi stouter and longer than P2, though sometimes not much so (Japan, Aleutian, 

 Hawaiian, and Galdpagos Islands to Tasmania, and westward to east Africa; 

 in the Atlantic north to the Bay of Biscay and the Caribbean Sea; chiefly in 



deep water, but a few species are subhttoral) Thalassometrinae (pt. 4) . 



/*. Cirri usually short, stout, and strongly curved, rarely more or less elongated, com- 

 posed of usually fewer than 25 segments, of which the distal are httle, if any, 

 shorter than the proximal and bear no dorsal processes, or at most a low blunt 

 tubercle at the distal end; surface of all the cirrus segments uniform in color and 

 dull; no transition segment; P, more slender than the succeeding pinnules, and 

 composed of shorter segments; Pa usually more nearly like P, than like P3 (Japan 

 to the Kermadecs and westward to east and south Africa; Caribbean Sea; sublit- 

 toral to abyssal) Charitometridae (pt. 4). 



^ Cavity in the centrodorsal containing the chambered organ and overlying structures large and 

 deep; rosette nearly or quite on a level with the dorsal surface of the radial pentagon, or the 

 basals, more or less reduced but not modified into a rosette, forming a ring between the 

 centrodorsal and the radials; only the interradial processes of the rosette form "spoutlike" 

 processes; central portion of the radial pentagon entirely open, with no calcareous dei)osit; 

 plane of the muscular fossae on the radial articular faces nearly or cpiite parallel with the 

 dorsoveutral axis; joint face elements distal to the transverse ridge strongly excavated, so 

 that they meet in the median line at an angle of about 90°; brachials from about the fourteenth 

 onward usually about as long as broad, and often longer than broad, very rarely broader than 

 long; second syzygy in the arms between brachials 9+10 or earlier; brachial syzygies close 

 together and regularly spaced; pinnules never prismatic; segments of the pinnules beyond 

 The third slender and usually much elongated, and the first 2 broadened; radials sometimes 

 10; arms very exceptionally more than 10 (occurring in all seas from the shore line to the 



greatest depths) Macrophreata (pt. 5). 



b'. Cirrus sockets with the borders unmodified; first syzygial pair oblong or squarish or slightly 

 wedge-shaped, and the brachials immediately following more or less oblong, 

 c'. Gonads developed wholly on the pinnules as fusiform or ovoid masses. 



dK Second postradial ossicle always axillary (occurring in all seas from the shore line to the 



greatest depths) Antedonidae (pt. 5). 



d'. No axillaries, each radial being followed by an undivided series of brachials (of general 

 occurrence, but absent from the Arctic and north and east Pacific; sublittoral to abyssal, 



but chiefly in deep water) Pentametrocrinidae (pt. 5). 



c*. Gonads lying on the arms at the base of the pinnules (shores of the Antarctic Continent and 



immediately adjacent regions; shallow to moderately deep water) _ Notocrinidae (pt. 5). 



b'. Cirrus sockets bordered ventrally by a horseshoe-shaped ridge, or flanked on either side by a 



high angular process; first syzygial pair very obliquely wedge-shaped, and the immediately 



following brachials triangular (Japan and Polynesia to the Indian Ocean; Brazil to the 



Caribbean Sea; northeast Atlantic; deep water) Atelecrinidae (pt. 5). 



AKTinCIAL KEY TO THE FAMILIES OF THE COMITULIDS 



'. Five arms only. 



6'. Centrodorsal low, much broader than high, thick discoidal or flattened hemispherical, with the 



cirrus sockets arranged in crowded rows; first syzygial pair oblong, or nearly so, followed by 



several more or less oblong brachials, which are succeeded by triangular brachials. 



c'. First 2 ossicles following the radials united by syzygy; lowest pinnule on the second ossicle 



following the radials and the next on the fourth, there being no pinnule on the third (vol. 



1, pt. 2, fig. 127, p. 79); arms short and tapering rather rapidly; centrodorsal a thick disk 



(vol. 1, pt. 2, fig. 190, p. Ill) (Japan to the East Indies and the Bay of Bengal; sublittoral) 



Eudiocrinidae (pt. 4). 



