PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 647 



Geographical range — The species of this subfamily occur in deep water everywhere 

 except in the Arctic seas (north of the Wyville Thomson ridge and 65° N. in Davis 

 Strait) and in the Mediterranean. 



Bathymetrical range. — From 28 to 5301 meters. 



The species of this subfamily are chiefly inhabitants of deep water. Of the 11 

 included genera, only one (Hathrometra) has been found in less than 50 meters. Seven 

 (Ilathrometra, Reiiometra, Phrixometra, Boleometra, Trichometra, Fariometra and 

 Thaumatometra) are found between 200 and 500 meters, while 8 occur in water of over 

 1000 meters. Five genera {Fariometra, Tonrometra, Trichometra, Thaumatometra and 

 Bathymetra) occur in water of more than 2000 meters; of these Tonrometra and Thauma- 

 tometra extend to over 3000 meters, while Bathymetra is only known at 4753 and 5301 

 meters. 



Several of the included genera are remarkable for their great vertical distribution. 

 Thus Thaumatometra ranges through 3093 meters, Trichometra tlu'ough 1937 meters, 

 Fariometra through 1990 meters, Hathrometra through 1755 meters, and Betiometra 

 tlirough 980 meters. 



Thermal range.— From -0.48° C. to +15.67° (?15.83°) C. 



The species of this subfamily are almost exclusively inhabitants of cold water. 

 The maximum representation is between 2° and 6°. Of the genera for which tempera- 

 ture records are available only one is found below 0° C. and only 2 {Hathrometra and 

 Trichometra) above 8°. 



It is interesting that the genus {Thaumatometra) with the greatest vertical range, 

 3093 meters, appears to have only a hmited thermal range, from 0.39° to 5.95°, or 5.56°. 



The maximum thermal range, 13.27°, is shown by Trichometra, though Hathro- 

 metra has a range of 11.89°. 



The thermal range of the other genera so far as we know, is very much more 

 restricted, that of Fariometra being 5.34°, of Betiometra 3.1°, and of Bathymetra only 

 0.78°. 



Characters. — The centrodorsal in the Bathymetrinae varies from conical, slightly 

 higher than broad at the base wath straight or slightly convex sides through rounded 

 conical to hemispherical and ev^en to much flattened and almost discoidal. It is 

 most commonly rounded conical to hemispherical, and from half again to twice as 

 broad at the base as high. 



In most species the numerous cirrus sockets, wliich may be as many as 100 in 

 number, but are usually between 25 and 50, almost completely cover the sides of the 

 centrodorsal. They are in most cases arranged in several closely crowded alternating 

 rows, those of succeeding rows decreasing very slowly in size toward the dorsal pole. 

 Sometimes they are less numerous and less crowded, and more irregular in their ar- 

 rangement, and the number of rows may decrease to about 3, or even to a single 

 irregular row of 10 to 15 sockets situated either about the dorsal pole or about the 

 periphery, as in Bathymetra. 



As a rule the bare dorsal pole is very small though in one species (Betiometra 

 alascana) it reaches a diameter of about a third that of the base of the ccntrodoi-sal. 

 It is ordinarily convex to more or less sharply pointed and smooth or nearly so. In a 

 few species it is roughened or pitted, in one {Thaumatometra mimiti-^sima) it bears 

 several rather long spines, and in another {Thaumatometra tenuiji) it is more or less 

 concave. 



