A MONOGKAPH OP THE EXISTING CRINOIDS 227 



in which the cirri are long and tapering with the outer segments longer than broad 

 and with only slight dorsal tubercles, including astyanax only; one hi which the outer 

 cirrus segments are broader than long but some of the earlier are as long as, or longer 

 than, broad, including affinis, pulchra, gravieri, singularis, compta, and madagascar- 

 ensis; and one in which all the cirrus segments are markedly broader than long, in- 

 cluding, reynaudi, amboinae, ater, and joubini. Some species are more or less on the 

 border line between the last two subgroups. Through H. astyanax the first section 

 of this group approaches very closely the genus Craspedometra, which possibly should 

 not be separated from it, and in another direction it also approaches the slender and 

 delicate Homalometra. Through H. compta, in which PI and P 2 are similar and of 

 approximately the same length, the second section approaches the genus Himerometra 

 as represented by H. persica and H. bartschi, though the brachial structure of the 

 species of Himerometra is most nearly like that of the next group. 



In the fifth and last group of the species of Heterometra, including philiberti, 

 sarae, parilis, africana, schlegelii, bengalensis, and flora, the brachials are exceedingly 

 short with parallel ends which become only slightly oblique on the earlier brachials. 

 Within this group there are two subgroups, one, including philiberti only, in which 

 IIIBr series occur and are wholly or mostly 4(3+4) instead of 2 as would be expected, 

 and another, including sarae, parilis, africana, schlegelii, bengalensis, and flora, hi 

 which, so far as is known, IIIBr series never occur. The species of this group are 

 evidently closely allied to the species of Amphimetra, and this relationship is empha- 

 sized by the occasional occurrence in some of them of fully grown individuals with 

 only 10 arms. They approach the species of Amphimetra through H. sarae in which 

 the earlier segments of the proximal pinnules have the carination reduced to a mere 

 sharpening of the side toward the arm tip. Their brachial structure, and especially 

 the occurrence of IIIBr 4(3+4) series hi philiberti, indicates that they also approach 

 the species of Himerometra, through H. persica and H. bartschi, more closely than 

 do the species of any of the other groups. 



Both of the species in the first group have a very limited range, H. savignii 

 occurring only from the Red Sea to Muscat, and H. nematodon being found only hi 

 Queensland and the Aru Islands. The single species of the second group ranges 

 from the Andaman Islands to the Philippines. The species of the third group occur 

 from the Maldive Archipelago to the Philippines and southward to northern Australia. 

 The species of the fourth group range from east Africa and the Red Sea to the Philip- 

 pines and southward to the Torres Strait region. The species of the fifth group are 

 found from east Africa to southern Japan, but are not represented in Australia. 



The species of Heterometra are all inhabitants of very shallow water and are most 

 abundant in a narrow band of a few meters' width just below the low tide mark. 

 One species has been recorded from a depth of 111 meters, and others from a depth 

 of 88 meters, but most of the records are for much shallower water. Indeed, of the 

 25 species only 4 (astyanax, pulchra, compta, and propinqua) have not been taken in 

 ordinary shore collecting. 



All the species are of medium or rather large size, but the largest of them are 

 not so large as the larger species of Himerometra, or as the species of Craspedometra. 



The species of Heterometra are among the most difficult of all comatulids to 

 identify. Most of those of which any considerable number of individuals are known 



