542 



THE AMERICAN NATURALIST [Vol. XLII 



Gulf of Maine, characterized by various genera belonging exclu- 

 sively to the Antedonidas, Heliometra occurring everywhere, 

 Hathrometra confined to the north, and Isometra to the south, 

 while Thaumatometra occurs in the south, but extends north- 

 ward in the Pacific to the Aleutian Islands; among the stalked 

 crinoids the Bathycrirms carpenterii type (B. carpenterii, B. 

 comphtnatus and B. australis) appear possibly to be peculiar 

 to the region; bathymetrically, the characteristic forms (except 

 Bathycnmis) are inhabitants of comparatively shallow water in 

 both polar areas, but dip downward to a considerable depth 

 when passing under the tropics; and (3) the Oceanic, which 

 occurs everywhere in moderate to very deep water with the 

 Indo-Paeific- Japanese, and extends thence over the entire ocean 

 area, except that it does not intrude into the area occupied by 

 the Polar-Pacific; the characteristic forms are the species of 

 Thalassometra having rounded and spiny rays and arm-bases 

 (such as T. bispinosa, T. vUlosa, T. gigantea, T. pubescent, T. 

 nwltispina and T. aster) and certain other species, such as T. 

 flava, T. porrecta and T. magnicirra, Stylometra, Bathymetra 

 and Charitometra, except the aculeata, hepburniana, basicurva 

 and tuberosa groups; of stalked crinoids, Rhizocrinus, Endoxo- 

 crmu.s. and the species of Batbycrinus, except the B. carpenterii 

 group, belong here ; the West Indian fauna falls almost wholly 

 in the last division, but there is a trace of Indo-Pacific-Japanese 

 influence, as, however, we might expect, since the entire Oceanic 

 fauna is a direct, though considerably modified, derivation from 

 it, even the well-known subgenera of Pentacrinitidae, Encrinus 4 

 an* Isocrmus being only a comparatively slight advance over 

 the apparently more primitive Metacrinus type. The Mediter- 

 ranean-northeast Atlantic fauna, characterized by Antedon 

 (.4. mediterranca, A. bifida and A. petasus) and Leptometra, 

 appears to be a localized offshoot from the Polar-Pacific 



Bearing these facts of distribution in mind we are not sur- 

 prised to find Ptilocrinus where Mr. Bather' found it for it 

 appears to be a genus of the Polar-Pacific area, and the same 

 Z-on« , .L tni b° f ° alam0CrinUS - Altho "£h Heliometra occurs 

 /•/wl/'~ ""'Y " S :IIV;l ' tw ° ;m ' ti( ' spwios, ghtc talis {=esch- 

 oidlYl- ,U / ll ,V / "'''' / ' Y ' / '' U ' th 1l " ir r, ' I>n ' S( ' ntatives in the Se » of 

 . m Y'. Ss ' iiml /m "' / '.'/"" , m) differ from the Antarctic 



eas aci c sj)ecies in the smoothness of their arms, and in 



