PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 287 



Bathymetrical range. — From shallow water, 1 1 meters and probably less, down to 

 1574 meters. 



Thermal range.— From —1.90° C. to +13.50° C; only /"/orome^m occurs in water 

 above 5.80° C, and only Florometra and, rarely, Heliometra occm- in water above .3.00° C. 



Characters. — The centrodorsal in the Heliometrinae is most commonly flattened 

 hemispherical with the small bare dorsal pole plane or more or less excavated, often so 

 much so as to form a deep pit; but in Solanometra it may be rounded conical while in 

 Anihometra it is usually, and in Promachocrinvs it is always, sharply conical with a 

 considerable apical portion of the cone bare of cirrus sockets. The cirrus sockets are 

 nmnerous, completely covering the sides of the centrodorsal from the ventral rim to 

 the edge of the bare polar area or polar pit, and are usuaUy arranged in from 4 to 7 

 closely crowded transverse rows; those of the succeeding rows decreasing very slightly 

 in size toward the pole; less frequently they are more or less isolated or less regular in 

 arrangement. 



The cirri in the various species of this subfamily are singularly uniform in structure, 

 and present almost no features by which genera or even species may be differentiated; 

 the cirri of Anihometra alone seem to be distinctive, though not very different from the 

 cirri of the other types, and the cirri of Promachocrinus possibly, on the average, could 

 be identified as such. 



The length of the cirri ranges from about 25 to 130 mm. or from 21 to 50 percent 

 of the length of the arms. They are shortest in Solanometra and longest in Anihometra 

 and Promachocrinvs though John (1938) has shown that the relative length of the 

 cirrus segments and hence of the cirri is very variable in P. kerguelensis. In Heliometra 

 and Florometra they measure about one third of the arm length. The relative length 

 of the cirri and arms in Promachocrinus is really not strictly comparable to the same 

 feature in Anthometra, since each arm of the latter equals two of the former. 



The number of the cirri varies from XXX-XXXV to L-CC, and in nearly all the 

 species is Ij-LXXX. Anthometra, in which the cirri are very long, has the fewest, but 

 the number of the cirri in the other genera is remarkably uniform. 



The nmnber of segments in the fully developed cirri varies from 25 to 90, with 

 the greatest frequency between 40 and 55, the small apical cirri usually have about 

 half as many segments as the peripheral. 



In form the cuTi vary but little; they are large and stout, strongly compressed 

 laterally and strongly recurved, excepting in Anthometra, in which genus they are more 

 elongated than elsewhere, more slender, and much less ciu-ved. About the margin of 

 the centrodorsal there are frequently seen very long and nearly straight cirri which 

 seem to function as tactUe organs. The cirri about the dorsal pole are usually about 

 half as long as the peripheral, and the intergradation between the two types is complete. 



The longest cutus segments are from half again to three times as long as broad, 

 or slightly longer, and are very slightly constricted centrally; the outer are shorter, 

 usuallj^ about as long as broad. As the segments begin to shorten, the median portion 

 of the distal border usually begins to project slightly, forming a more or less obvious 

 terminal dorsal spine. The segments of the small apical cirri are much more uniform 

 in size than those of the longer cirri. 



Low and broadly rounded tubercles may represent the ends of rudunentary 

 basal rays in the interradial angles, but are not often present. 



