A MONOGRAPH OF THE EXISTING CRINOIDS 27 



(2) The Polar-Pacific, including the Arctic and Antarctic circumpolar areas, 

 and the entire American coast of the Pacific frora Bering Straits to the Straits of 

 Magellan, the coasts of eastern Asia to southern Japan (where it meets the preceding 

 at Tokyo Bay), including the Sea of Okhotsk and the Sea of Japan, and the Atlantic 

 coasts south to near the Hebrides and the Faroe Channel, and to the Gulf of Maine, 

 characterized by various genera belonging exclusively to the Antedonidae, Helio- 

 metra occurring everywhere, Hathrometra confined to the north, and Isometra to the 

 south, while Thaumatometra occurs in the south but extends northward in the Pacific 

 to the Aleutian Islands; among the stalked crinoids the Bathycrinus carpenterii type 

 {B. carpenterii, B. complanatus, and B. australis) appear possibly to be pecuUar to 

 the region; bathymetrically the characteristic forms (except Bathycrinus) are in- 

 habitants of comparatively shallow water in both polar areas, but dip downward to 

 a considerable depth when passing imder the tropics. 



(3) The Oceanic, which occurs everywhere in moderate to very deep water with 

 the Indo-Pacific-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. villosa, T. gigantea, T. pubescens, T. multispina, and T. 

 a^ter) and certain other species, such as T. jlava, T. porrecta, and T. magnicirra, 

 Stylometra, Bathymetra and Charitometra, except the aculeata, hepburniana, basicurva, 

 and tuberosa groups; of stalked crinoids, Rhizocrinus, Endoxocrinus, and the species 

 of Bathycrinus, except the B. carpenterii group, belong here. 



It is stated that 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 (the subgenus 

 Cenocrinus of Wyville Thomson; see beyond) and Isocrinus being only a compara- 

 tively shght advance over the apparently more primitive Metacrinus type. 



The Mediterranean-northeast Atlantic fauna, characterized by Antedon (A. 

 mediterranea, A. bifida, and A. petasus) and Leptometra, appears to be a locahzed 

 offshoot from the Polar-Pacific fauna. 



It is pointed out that while Heliometra occurs throughout the Polar-Pacific area 

 the two Arctic species, glacialis ( = eschrichtii) and quadrata (with their representatives 

 in the Sea of Okhotsk, maxima and brachymera) differ from the Antarctic and east 

 Pacific species in the smoothness of their arms and in a different distribution of the 

 brachial syzygia. 



In a paper published in November various questions converning the ecology of 

 the recent crinoids are considered. 



In very shallow water Antedon bifida is usually about 120 mm. in expanse, while 

 individuals from deep water are 220 mm. or more across. This is explained by 

 supposing that throughout the range of this species the very small pelagic organisms 

 and minute crustaceans which serve as food are when living more or less evenly 

 distributed, but with increasing depth the supply of dead falling to the bottom 

 increases in intensity, resulting in a progressively greater food supply. 



In general the size of crinoids gradually increases to 100 fathoms, from 100 to 

 about 600 fathoms remaining uniform, and below 600 fathoms gradually decreasing 



