214 ABYLINAE. 



lateral ridge, in addition to the ventral angles. In one species, trigona, in which 

 the nectophore has been described as trigonal, the right lateral ridge is nearh- 

 but not altogether, suppressed. In one, bassensis, the dorsal ridge is entirely 

 lacking, and in the latter alone is the hydroecium a closed tube. Thus, although 

 the nectophore of bassensis is truly tetragonal as Haeckel supposed, we can not 

 draw any sharp line between the "pentagonal" nectophore, e. g. of tetragona, 

 and the "trigonal" one of trigona; therefore the structure of this nectophore 

 alone would justify only two groups, bassensis being opposed to all the other 

 species. 



When we study the anterior nectophore, we find that so far as it is concerned, 

 the Abylinae fall into two main groups. In the one are leuckartii, trigona, and 

 haeckeli, which agree in that the nectophore has a rectangular apical facet, and 

 in the general arrangement of facets and ridges, the only difference of much 

 importance between them being that the simple ventrolateral facet of leuckartii 

 is subdivided in the other two species by a transverse ridge. This may be called 

 the "trigona" tj'pe. In the other group are tetragona, eschschoUzii, and bassensis 

 in which the nectophores, distinguishable from one another only by minutiae 

 of form, have no apical facets, the lateral ones of the two sides joining apically 

 in a ridge. 



It is evident that while the use either of the anterior or of the posterior 

 nectophore as the prime factor in generic subdivision results in two groups of 

 AbyUnae, the hne of demarcation between the two differs, according as we 

 choose one or the other nectophore as our guide. On a priori grounds we might 

 expect that the anterior one, being phylogenetically the older, might be the 

 more important, and this view is supported by the structure of the bract. It 

 appears that Haeckel was in error in drawing a parallel between the bract and 

 the posterior nectophore in all cases, because the "Amphiroa" type, instead of 

 being restricted to species with apparently trigonal lower nectophore as he 

 supposed, is also found in one species, leuckartii, in which both dorsal and lateral 

 ridges are well developed in the posterior bell. But the two other species 

 which agree with the latter in the pentagonal form of the posterior nectophore, 

 have very different bracts, namely the "Aglaisma" type. Bassia bassensis 

 alone is distinguished from all other Abylinae by the structure of both posterior 

 nectophore and bract. In comparing the bract with the anterior nectophore, 

 we find a close correspondence in place of the confusion just outlined. Thus 

 in all species with the "trigona" type of anterior nectophore (including leuc- 

 kartii, as I have determined, p. 218), the bract is an "Amphiroa." And of the 



