62 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



eye, in the upper part of the ganglion, is an accessory mass of optic 

 cells, very similar to that seen in the aggregated forms of Salpa cylin- 

 drica (figs. 87, p. 98, and 89, p. 99), S . fusfiformis (fig. 79, p. 92), and 

 Apsteinia punctata (figs. 56, p. 77, and 57, p. 78). 



RITTERIA HEXAGONA (Quoy and Galmard, 1824). 



Salpa hexagona Quoy and Gaimard, 1824. 

 (?) S. biennis de Blainville, 1827. 

 Iasis hexagona Herdman, 1891. 



This species is somewhat unlike the other Ritterias, and the appro- 

 priateness of its inclusion in the same subgenus is perhaps doubtful. 

 The numerous wide irregularly united muscle bands and the loosely 

 looped gut, in the solitary form, and the rather decided asymmetry of 

 the aggregated zooids have, however, seemed sufficient to justify such 

 classification. 



I have abundant material of both solitary and aggregated forms 

 of this species which has been studied by a number of zoologists. 

 Streiff, who has done such accurate work on the muscles of many 

 species, has not observed this form. The drawings here given are 

 after Traustedt (1885) and Apstein (1894, b) and from specimens in 

 the collections of the United States Bureau of Fisheries and the United 

 States National Museum, which include many individuals of both 

 solitary and chain forms from Philippine waters and the northern 

 Pacific Ocean off Alaska. 



The following specimens are in the collection of the United States 

 National Museum : 



Cat. No. 6428, U.S.N.M. (solitary lorm), Albatross station D 5258, 

 Juraojurao Island, off southern Panay; June 2, 1908; surface; sur- 

 face temperature, 84° F.; surface density, 1.02587; one specimen. 



Cat. No. 6458, U.S.N.M. (embryo) , Albatross station D 5128, Nogas 

 Island, Sulu Sea; February 4, 1908; surface; surface temperature, 

 80° F.; one specimen. 



Cat. No. 6455, U.S.N.M. (aggregated form) , Albatross station D 5196, 

 Capitancillo Island, off northern Cebu Island; April 3, 1908; surface; 

 surface temperature, 82° F.; surface density, 1.02518; three speci- 

 mens. 



Cat. No. 6516, U.S.N.M (aggregated f orm) , Albatross station D 5128, 

 Sulu Sea, vicinity Southern Panay, Philippine Islands, February 4, 

 1908; surface; surface temperature, 80° F.; 60 plus specimens. 



Cat. No. 6531, U.S.N.M. (solitary form), Albatross station D 5350, 

 Palawan Passage, Philippine Islands; December 27, 1908; surface; 

 surface temperature, 80° F.; surface density, 1.02381; one specimen. 



Cat. No. 6539, U.S.N.M. (aggregated forms), Albatross station D 

 5128, Sulu Sea, vicinity southern Panay, Philippine Islands; February 

 4, 1908; surface; surface temperature, 80° F.; three specimens. 



