CLARK: CRINOIDS. 



247 



flattened against each other; centro-dorsal hem- 

 ispherical or discoidal, the cirri without definite 

 arrangement ; cirrus segments fairly uniform 

 throughout, one or more always markedly 



" dice-box shaped ; " 10 arms 



Antedon de Freminville, 1811, (Asterias bifida Pennant). 

 ee. all the pinnules, especially the lower, greatly 

 elongated, the latter composed of greatly elon- 

 gated segments of which the first, like those 

 following, is greatly elongated ; centro-dorsal 

 conical or columnar, with 5 broad inter-radial 

 areas or ridges dividing it into five radial 

 areas, each with definite vertical rows of cirrus 

 sockets ; 10 arms. 

 f. costals and lower brachials smooth, well 

 separated, and rounded, cirri smooth, with 

 all the segments elongated, arranged in 

 3, 4, or 5 vertical rows in each radial 

 area. 

 Psathyrometra (Antedon frag His A. H. Clark). 

 ff. costals and lower brachials in close ap- 

 position and strongly " wall-sided " ; cirri 

 with much elongated segments proxi- 

 mally, very short and spiny segments 

 distally, arranged in two vertical rows 



in each radial area 



Zenometra (Antedon columnaris P. H. Carpenter). 

 ccc. lower pinnules cylindrical, one or more very stout, styli- 

 form, and more or less elongated. 

 d. cirri with 50-70 short segments, bearing stout spines 

 distally ; first pinnule only enlarged, greatly elongated ; 

 following pinnules very short, in abrupt contrast ; 

 costals and lower brachials with straight sides, the 

 former rounded and widely separated ; brachials tri- 

 angular or quadrate, rather long ; 40-60 arms . . . 

 Pontiometra (Antedon andersoni P. H. Carpenter). 

 dd. cirri with 15-40 subequal short segments; the en- 

 larged lower pinnules followed by pinnules of inter- 

 mediate character. 



e. cirri irregularly placed on a discoidal centro- 

 dorsal ; costals and lower brachials with con- 

 vex sides, giving them a characteristic swollen 

 appearance ; brachials short, mostly oblong or 



short-quadrate ; 10-50 arms 



Himerometra (Antedon crassipinna Hartlaub). 

 ee. cirri in ten vertical rows on a conical centro- 

 dorsal ; costals and lower brachials with 

 straight sides; brachials long; 10-15 arms. 



