TWO SPECIES OF HYDRACTINIA 
489 
doubt that the corresponding parts are homologous in a general 
way, but it would be in my opinion a mistake to look upon these 
forms with complex skeleton as more nearly related to each other 
than to those without it. To clarify this point a much more 
detailed knowledge of the structure and development of these 
forms than we possess at present appears to me necessary. So 
far as I can see at present the development of a complex skele- 
ton in these forms appears to have gone on independenth^ in 
the different species; in other words, the resemblance is one of 
homoplasy. As to the relationships of the fossil forms mentioned 
by Carter^^ and Steinmann (73), I have nothing to sa3^, because I 
have not been able to study them. So far as I can see from the 
descriptions, however, their affinities to the living hydroids appear 
to me to be more remote than is supposed by Carter and Stein- 
mann, with the exception of the species of Hydractinia. 
2. HYDRACTINIA SPIRALIS, N. SP. 
I can deal very briefly with this species, because the gonophores 
appear to be in all essential respects exactly like those of the pre- 
ceding species. The form was first described by Inaba'^ as a 
species of Podocoryne as follows : 
3. Podocoryne sp. (figs. 5, 6, 7,). 
Trophosome. — Hydrorhiza consisting of numerous parallel small 
tubes, the perisarc covering them being fused to^^ether and forming a 
strong lamella. From this lamella spring small pointed chitinous 
spines. Hydranths also springing in large numbers from the lamella; 
they are of two forms, those without reproductive organs large and 
with 12-18 tentacles; those bearing reproductive organ? small and 
with 4-8 tentacles. 
Gonosome. — Medusoid, growing from the hypo-tentacular part of 
the hydranth; imperfectly developed and incapable of swimming, merely 
with four radial canals and a circular; manubrium, however, full of 
genital cells, enlarged and entirely filling the cavity of the umbrella. 
Color. — Hvdranth colorless; perisarc reddish brown. 
^* Loc. cit. riS, p. 2. 35 Loc. 77, and 78. »» Inaba: '09, p. 98. 
