TROPICAL PACIFIC HOLOTHURIOIDEA. 153 



The Echini were represented by forty species, a very large number in pro- 

 portion to the total number of species known. There is no means of determin- 

 ing how many specimens were taken as there are no available records on this 

 point. Ten of the species brought home are common littoral species of wide 

 range but of the other thirty, no fewer than twenty-nine were new when taken 

 and all but one of these is from deep water. Undoubtedly the most remarkable 

 sea-urchin discovered is Pilematechinus rathbuni, but Cenlrocidaris doederleini, 

 Dialithocidaris gemmifera, Plexechinus cinctus, and Phryssocystis aculeata are 

 also of exceptional interest, each being the type of a new genus. 



The Holothtjrians were the most generally met with of any of the classes 

 of echinoderms and the records show that 953 were in the collections brought 

 home. These represented seventy-nine different species many of which are com- 

 mon littoral forms of wide range but forty-three w T ere described as new. Of 

 course the most remarkable is the extraordinary Pelagothuria natatrix, sole 

 representative of a pelagic family and the only echinoderm known to be truly 

 pelagic in adult life. Other noteworthy holothurians, knowledge of which we 

 owe to these explorations of the Albatross, are two abyssal species of Myrio- 

 trochus, the huge Psychropotes raripes, Laetmophasmafecundum, Capheira sulcata, 

 and Echinocucwnis bitentaculata. 



Summing up for the five classes, we find that the Albatross, on her three 

 Tropical Pacific expeditions, collected several thousand echinoderms, repre- 

 senting 315 species, of which 207, or more than two thirds, were new. The 

 increase in our knowledge of the morphology and distribution, both geographi- 

 cal and bathymetrical, of the group, which we owe to these expeditions, cannot 

 be summarized in this rough and ready way, but one cannot turn the pages 

 of the following reports, wherein they are treated, without realizing how great 

 it is. 



List of the Reports based wholly or in part on the Echinoderms collected by the 

 Albatross Tropical Pacific Expeditions in 1891, 1S99-1900, and in 



1904-1905 



Crinoids. 



A. Agassiz, 1892. Mem. M. C. Z., 17, no. 2, p. 1-95, pi. 1-32. 



C. Hartlaub, 1895. Bull. M. C. Z., 27, p. 127-152, pi. 1-4. 



A. H. Clark, 1908. Bull. M. C. Z., 61, p. 231-248, pi. 1, 2. 

 Asteroids. 



H. Ludwig, 1905. Mem. M. C. Z., 32, 304 pp., pi. 1-36. 



