232 DIPHYABYLA HUBRECHTI. 



forming a single tooth. The facets are thus a triangular dorsal, a dorsolateral, 

 and a ventrolateral on each side, and a fusiform ventral. The ridges all termi- 

 nate in prominent triangular teeth at the base. The hydroecial opening lies high 

 above the opening of the nectosac (Plate 12, fig. 7). The nectosac extends 

 apically far beyond the level at which the pedicular canal joins it, and conse- 

 quent on this prolongation its dorsoradial canal follows a Diphyid rather than 

 an Abylid course (Plate 12, fig. 7). The other canals present no features of special 

 interest. In the "Siboga" example the nectosac was narrow and tubular for the 

 last part of its course. But in our example it terminates bluntly slightly above 

 the level at which the ventral ridges branch. This apparent difference is 

 probably due to the distortion of that region mentioned by Lens and Van 

 Riemsdijk (:08). This same level marks the beginning of the apical projection 

 (Plate 12, fig. 7). This is bent; but as the bending is dorsad in the "Siboga," 

 ventrad in the "Albatross" specimen, it is probably an accidental distortion. 



To derive the pyramidal form of Diphyabyla from the rectangular necto- 

 phore of Abyla leuckartii, all that is necessary is to imagine the apicodorsal 

 angle of the latter, with the apex of the nectosac, drawn out into a triangular 

 point. The dorsal facets of the two correspond ; but the ventral of the Diphya- 

 byla represents both the ve ntral and the rectangular apical facets of A . leuckartii. 

 It is true that the transverse ridge separating the two in the latter is unrepre- 

 sented in the former, but the presence or absence of the ridge is a very minor 

 matter, depending on whether the ventral facet is straight as in Diphyabyla 

 or bent at a right angle as in A. leuckartii. It is entirely comparable to the 

 transverse ridge which subdivides the ventral facet in A. haeckeli, but is absent 

 in the closely related A. trigona. 



The somatocyst is large, oval, and extends basally from its connection with 

 the hydroecium, as in Abyla leuckartii. The ventral ridges in the two follow 

 the same course, particularly in their basal junction, as do the lateral ridges 

 except for the fact that in A. leuckartii they terminate a short distance above 

 the lateral teeth (Plate 13, fig. 5) instead of reaching the basal margin as in 

 Diphyabyla. The basal teeth likewise correspond in both species. The corre- 

 spondence in such minor details as the basal teeth and in the degree of serration 

 is of great interest from the phylogenetic standpoint for it points in an unmis- 

 takable manner not only to the genus, Abyla, but even to the particular species, 

 {. e. leuckartii, from which Diphyabyla is descended. The Abylid affinities of 

 Diphyabyla are so close that the subfamily Diphyabylinae of Lens and Van 

 Riemsdijk is unnecessary (p. 215). To preserve it would only obscure the rela- 



