THE SIPHONOPHOEA. 34,3 



111 H. pllcata the nectophore is short and broad, and the hydroecium, which is very 

 deep, occupies only about one-third of the ventral surface. In P. cymhiformis, however, 

 as is clearly shown in Gegeubaur's (1854) excellent figures, the nectophore is propor- 

 tionately longer, and the hydroecium extends for its whole length, in the form of 

 a groove. When specimens of the two species are placed side by side, these differences, 

 which (though, of course, of minor importance) prove to be constant, are at once 

 apparent. [Compare also the figures of R. lilicata ( = P. diphjes) by KoUiker, 1853 a, 

 with those of P. ci/iiibiformis (^P. maxima) by Gegenbaur, 1851.] 



The terminal dilatation of the somatocyst in JR. piicata, lately mentioned as a specific 

 character by K. C. Schneider (1898), also proves to be constant. Although the 

 contraction of preserved material may obscure it, it is more or less prominent in all the 

 Biscayan specimens, and was observed and figured by KoUiker and by Vogt, as well 

 as by Quoy and Gaimard, but it has never been recorded, nor have I observed it, in 

 P. cymhifonnis. 



The appendages are too fragmentary to enable me to add to the earlier descriptions 

 of these structures noted above. In its form, the single special nectophore which was 

 still preserved agrees clearly with Vogt's figures. 



The inferior (older) nectophores are proportionately somewhat shorter and broader 

 than those of P. cymbifortnis. The difference is so slight, however, that the two might 

 be easily confused in the absence of their respective superior nectophores. The form of 

 the hydroecium in B. piicata is well shown in Vogt's figure (1851, pi. 16. fig. 3). 



Tlie entire absence of this species from any of the surface hauls, the comparatively 

 great depths of the hauls in which it was taken, and the positive evidence of its 

 capture in one closing-net haul between 300 and 200 fathoms, show that at least in the 

 Bay of Biscay, at the time of the expedition of the ' Hesearch,' it was a member of 

 the mesoplankton, not of the epiplankton. But, inasmuch as it has been recorded 

 previously from the surface on many occasions, its presence at a lower level cannot 

 be regarded as indicating an invariable habitat. 



DiPHYOPSiNiE, Haeckel, 1888. 

 DiPHTES, Cuvier, 1880. 



DlPH^ES STJBTILIS, Chun. 



Erscea elongata, Will, 1844, p. 8.2, Tab. 2. figs. 30. 31. 



Monophyes irregularis (partim), Chun, 1885, p. 271, Taf. 2. fig. 3 (non Clans, 1874). 



Moniiphyes gracilis (partim), Chun, 1885, p. 271, Taf. 2. fig. 5 (non Claus, 1874). 



Diphyes subtilis, Chun, 1886, p. 449 ; 1897 b, p. 103 ; Lens & Van Riemsdijk, 1908, p. 47. 



Monophyes diptera, Haeckel, 1888, p. 129. 



Diphyes elongata, K. C. Schneider, 1898, p. 85 (non Hyndman, 1841, p. 165). 



OccuiTcnces : 25 to fathoms ; 31 a. 1 anterior nectophore. 

 75 to fathoms; o2g. 1 anterior nectophore. 



100 to fathoms ; 24 d, 32 d, 32 jj, 35 b, 30 b. 17 anterior nectophores ; 

 all about 5 mm. long. 



