CLARK: THE CRINOID FAMILY ANTEDONIDAE 507 



P 2 with the third segment broader than long, and the fourth broader 

 than long, or about as long as broad (Caribbean Sea, and north- 

 ward to North Carolina; 13-1029 meters) Coccometra 



Subfamily PEROMETRINAE A. H. Clark 

 Key to the Genera of the Subfamily Perometrinae 



Pi and P a absent; size small, the 10 arms being from 25 mm. to 35 mm. 

 (usually between 25 mm. and 30 mm.) in length; cirri XX- 

 XXX, 22-25, 10 mm. long (West Indies; 59^33 meters) 



Hypalometra 

 Pi always present, though P a (on the inner distal end of the first 

 syzygial pair) is sometimes absent. 

 Ossicles of the IBr series and first two brachials with smooth and 

 umrodified depressed borders, laterally in close apposition 

 with their neighbors and sharply flattened against them; 

 synarthrial tubercles (on the articulations between the ele- 

 ments of the IBr series and first two brachials) very promi- 

 nent, sometimes extravagantly developed; Pi is as long as, 

 longer than, or shorter than, P 2 ; P may be absent; 10-14 

 (usualfy 10) arms from 35 mm. to 90 mm. long 28-55 cirrus 

 segments (From Madagascar to the Kei Islands and south- 

 ern Japan; 70-252 [?273] meters) Perometra 



The ossicles of the IBr series and first two brachials may be just 

 in contact laterally, but their sides are never sharply flat- 

 tened, and prominent synarthrial tubercles are never de- 

 veloped; their lateral borders always bear tubercles, one or 

 many to each ossicle, and their distal and proximal borders 

 are usually prominently everted and tubercular. 

 Interbrachial portions of the perisome naked; P always pres- 

 ent (Kei Islands and southern Japan; 204-344 meters) 



Nanometra 

 Interbrachial portions of the perisome with numerous promi- 

 nent rounded calcareous nodules which are not in lat- 

 eral contact; P usually absent (Moluccas and southern 

 Japan; 99-270 meters) Erythrometra 



Subfamily HELIOMETRINAE A. H. Clark 

 Key to the Genera of the Subfamily Heliometrinae 



10 raclials and 20 arms (coasts of the Antarctic continent, and Kerguelen 



Island; 18-400' meters) Piomachocrinus 



5 raclials and 10 arms. 



Each brachial bears a high median carinate process; Pi much 

 longer than P 2 (Coasts of the Antarctic Continent; 223-400 



[?900] meters) Anthometra 



No carinate processes on the brachials. 



Brachials very short, much broader than long; middle and 



