REPORT ON THE CRINOIDEA. 31 



The distribution of the two leading Comatula genera, Antedon and Actinometra, 

 cannot yet be fully worked out, owing to the large number of species which are still 

 undescribed ; but that of the other generic types is easily stated. 



The archaic Thaumatocrinus has only been found at 1800 fathoms at Station 158 

 in the Southern Ocean, where it was associated with Promachoerinus abyssorum, which 

 also occurred at Station 147 (1G00 fathoms), together with three species of Antedon. 

 Another species of Promachoerinus is common at Kerguehm, and a third was obtained at 

 500 fathoms off the Meangis Islands. Three species of Atelecrinus are known, two from 

 the Atlantic and one from the Pacific. The unique specimen of the latter was found at 

 Station 174c in the South, Pacific, at 610 fathoms ; while one of the Atlantic species 

 is only known from Pourtales' dredgings in the Gulf Stream off Havana (450 fathoms). 

 The other, found by the Challenger in 350 fathoms at Station 122 off Pernambuco, was 

 subsequently met with by the " Blake " off Nevis, St. Lucia, and Granada, at depths 

 of 291 to 422 fathoms. 



Eudiocrinus, first obtained in quite shallow water among the Philippines by Semper, 

 was dredged by the Challenger both in the North and in the South Pacific, at depths 

 varying from 565 to 1050 fathoms; while the " Travailleur " found Eudiocrinus 

 atlanticus at 896 metres in the Bay of Biscay. 



In discussing the distribution of Antedon and Actinometra, the two principal genera 

 of Comatulse, it must be remembered that each of them, but especially Antedon, contains 

 a very large number of species, and they should be considered for this purpose to 

 represent subfamilies rather than genera. Thus, for example, the name Antedon is now 

 given to all recent endocyclic Comatulse with the basals metamorphosed into a rosette, 

 and five rays bearing ten or more arms, just in the same way as the name Echinus was 

 originally used for a variety of regular Urchins, which have now received different generic 

 names. The difference between the tiny ten-armed Antedon abyssicola inhabiting depths 

 of three miles and upwards in the Pacific (PI. XXXIII. figs. 1, 2), and the littoral Antedon 

 clegans, Antedon multiradiata, or Antedon regalis (Pis. VIIL, IX., XLVL), is no doubt 

 very considerable at first sight ; but there are so many intermediate links between the 

 simple and the complex forms, that no hard and fast generic lines can be drawn. At the 

 same time, a glance at the tabular keys to the species which are given in the following 

 pages will show that they fall into certain very well defined groups ; and the range of 

 each of these groups, both in depth and in space, may be profitably studied. 



In the first place, all the species of Antedon which have the two outer radials united 

 by syzygy are limited to quite shallow water in the En stern Archipelago. They are 

 comparatively few in number, and have perhaps the most restricted geographical range of 

 any of the specific groups. On the other hand, the Antedon species of the simple ten- 

 armed type like Antedon rosacea, are most remarkably abundant, and also extremely 

 varied in their character, — Antedon abyssicola and Antedon tuberosa, or Antedon 



