CHAP, v.] GENERAL CONCLUSIONS. 297 



by forms more or less nearly allied to Astropecten, Astrogonium, 

 Archaster, Pteraster^ and Hymenaster, abounded at all more 

 moderate depths; and the singular aberrant genus Brisinga 

 was found universally from the coast of Labrador to the Ant- 

 arctic ice -barrier, at all deptlis, from 400 to 3000 fathoms, the 

 trawl rarely coming up from deep water without some frag- 

 ments of its fragile arms. 



The novel forms of sea-urchins, regular and irregular, are 

 numerous and highly interesting, especially in their paleonto- 

 logical aspect. Species of the genera Porocidaris and Salenia 

 occur not unfrequently, and the curious flexible Echinothuridse 

 have assumed the proportions of an important family. Among 

 the irregular urchins the relation between the modern abyssal 

 fauna and the fauna of the later Mesozoic beds is even more 

 marked. A number of genera hitherto undescribed associate 

 themselves with the chalk genus Tnfulaster, while others And 

 their nearest allies in Micrmter and Ananehytes. 



The Holothuridea are very generally distributed down to 

 the greatest depths ; and are represented in deep water by a 

 peculiar series allied to Psolus, with a very distinct ambulatory 

 disk, very frequently a great development of calcified tissue 

 in the perisom, and frequently symmetrical series of long tabu- 

 lar appendages along the back and sides. These Holothtirice, 

 which are among the most characteristic of the abyssal forms, 

 have not yet been critically examined. 



Polyzoa were found at all depths : some extremely beauti- 

 ful and delicate forms, referred principally to the Bicellariadse 

 and to the Salicornariadse, occurred at depths between 2000 

 and 3000 fathoms in sterile regions where other animal life 

 was scarce. 



The Gephyrea yielded a few interesting undescribed forms. 

 Annelids were not abundant at great depths; but on one or 

 two occasions — as, for example, at Station XIX., on the section 

 between Teneriffe and Sombrero — their occurrence was of spe- 

 ll.— 20 



