PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 291 



or low rounded conical centrodorsal, the distal edges of the brachials and pinnulars 

 spinous, the third syzygy situated between brachials 14+15, P 4 markedly shorter than 

 Pa, and relatively few, not more than 41, cirrus segments, seems to be somewhat less 

 specialized than the other two. 



In Heliometra the brachials beyond the third syzygy, which is between brachials 

 14 + 15, are triangular and about as long as broad with smooth distal ends, the dorsal 

 pole of the centrodorsal is flat or slightly concave, and P 4 and even P 5 may be as long 

 as P 3 , with P 8 much shorter. 



In Florometra the brachials just beyond the third syzygy, which is often displaced 

 distally to between brachials 16 + 17, are more or less wedge-shaped and very rarely 

 so long as broad, usually markedly broader than long, with spinous ends, the dorsal 

 pole of the centrodorsal is deeply excavated, and all the pinnules from PI to P 6 may 

 be modified as oral pinnules. In this genus only is there a tendency toward the de- 

 velopment of IIBr series, though a specimen of Heliometra glacialis maxima has been 

 reported with an axillary radial. 



The frequent distal displacement of the third syzygy, the shortness of the brachials, 

 the greater number of oral pinnules in fully developed individuals, the excavation of 

 the dorsal pole of the centrodorsal, and the tendency toward a development of IIBr 

 series seem to indicate that Florometra represents a higher degree of specialization than 

 Heliometra. 



[NoTE BY A.M.C.] In checking Mr. Clark's key to the genera of Heliometrinae 

 following the introduction of several new species of Florometra, several alterations were 

 found to be necessary, particularly with regard to Florometra, Heliometra and Solano- 

 metra. Measurements of the proximal brachials of specimens of ah 1 three genera sug- 

 gested that Heliometra is intermediate between the other two in the thickness of the 

 arms as well as in the proportions of the pinnule and cirrus segments. These three 

 genera are very closely related and can only be recognized by a combination of minor 

 characters, some of which tend to vary according to the size. 



KEY TO THE GENERA OP HELIOMETRINAE 



[Modified by A.M.C.] 

 a 1 . 5 radials and 10 arms. 



6 1 . Arms rounded dorsally, sometimes with a transverse spinous crest but never carinate; P 2 similar 



in size to PI. 



c 1 . Arms relatively narrow, the width at the first syzygy about 2.5 mm. when the length of the 

 division series and first nine brachials together is about 15 mm.; segments of the middle and 

 distal pinnules longer than broad, often quite elongated; the longest cirrus segments may 

 be over twice as long as broad; division series and brachials usually more or less spinous 

 (Korean Straits and Japan, north to the Bering Sea, south along the west coast of the 

 Americas to the Cape Horn area and the Southern Ocean; 11-1574 meters). 



Florometra (p. 292) 



c 2 . Anns moderate in width, the first syzygy being usually 2.8 to 3.0 mm. wide when the length of 

 the division series and the first nine brachials together is about 15 mm.; segments of the 

 middle and distal pinnules not much longer than broad; the longest cirrus segments rarely 

 as much as twice as long as broad; in specimens of arm length less than 100 mm. the division 

 series and first few brachials may be finely spinous but larger specimens are always smooth 

 (Arctic Seas south to Cape Cod, Iceland, the Faroes, northern Norway and off the northern 

 Siberian coast, also in the Pacific from the Okhotsk Sea to the Korean Straits; 14-1358 

 meters) Heliometra (p. 340) 



