No. 12. — Reports on the scientific results of the Expedition to the Eastern 

 Tropical Pacific, in charge of Alexander Agassiz, by the U. S. Fish 

 Commission Steamer "Albatross," from October, 1904, to March, 

 1905, Lieut. Commander L. M. Garrett, U. S. N., Commanding. 



XXVI. 



The Ctenophores. 



By Henry B. Bigelow. 



The " Albatross," during her cruise in the Eastern Tropical Pacific, 

 1904-1905, collected only six species of Ctenophores, none of which 

 are new. But the series is of greater interest than the paucity of its 

 members would suggest, because up to the present time we have had 

 almost no data of the fauna of the region and because the genus Hormi- 

 phora is represented by a series so large that it throws new light on 

 the interrelationships of the various described species. The oppor- 

 tunity to study the material fresh from the net, which I owe to Mr. 

 Agassiz, has been of great assistance. 



CYDIPPIDA 



PLEUROBRACHIIDAE Chun. 



Pleurobrachia Flemming. 



Two Atlantic species of this genus are generally recognized, pileus 

 known from both sides of the north Atlantic, and the Mediterranean 

 rhodopsis, while Moser (:09) has recently described a third, crinita, 

 from Greenland. Mayer (:12) describes a fourth, P. brunnea, but 

 this is probably identical with Hormiphora spatulata Chun (p. 377). 

 From the Indo-Pacific two species, globosa Moser and pigmentata 

 Moser, are listed by Moser ( : 09) who has most recently surveyed the 

 genus. Pleurobrachia pileus, P. rhodopsis, and the Pacific form 

 described by A. Agassiz ('65) as P. bachei are very closely allied to 

 one another. Moser ( : 09) considers bachei a synonym of pileus. 

 The exact relationships of these forms have not been clear, partly 

 because the Mediterranean form is known only from Chun's account 



