Aiistralian Hydroids. 329 



There are usually about 22 tentacles, which, fully expanded, reach 

 ^bout .60 mm. in length. 



In my specimens of S. camjxuiularia the proboscis, wliich 1 liave 

 ^iescribed as an annular band bordering the calyx, is nairower 

 than in the present species, and it is spread outward nearly liori- 

 iontally; in tliose specimens, however, the tentacles are mostly 

 reverted, besides being contracted, and 1 have had no opportunity 

 of observing well-preserved specimens. 



Note on the relationsliips of Silicularia, Okthopyxis and 



BONNEVIELLA. 



In the last paper of this series I have referred to the " annular 

 l>and " of Siliculdria as the homologue of the proboscis of 

 Orthopyxis; the study of «S'. undulata, however, and comparison 

 -with several species of Orthopyrii<, has satisfied me that tlie two 

 genera are, in regard to the form of the hypostome, really identical 

 in structure. The specimens of Orfhopyris which were most favour- 

 able for examination belonged to the forni which I have called 0. 

 ^anf/ulafa, but I was able to satisfy myself that other species, in- 

 cluding 0. caliculafa, were of the same type, the hypostome being 

 formed, in its lower half, by the tentacular calyx, with its cellular 

 lining, and in the upper half by the free extension or outgrowth of 

 the same, wliich constitutes the proboscis. Whether the external 

 band of granular material whicli I have noticed a.s encircling the 

 proboscis in S. undulata is present in Orthopy rii^ was, however, 

 not discernible in the specimens, wliicli were by no means in so 

 favourable a condition for examination as the Silicularia. 



Tliat so well known a species as 0. caliculfffa should prove so 



-different in the character of its hypostome from the other forms 



•(such as Obelia) with Avhich systematists generally class it, was an 



unexpected result, as even Agassiz, in his study of this species, 



states that the structural elements are the same as those of most 



campanularians (including Obelia). On referring, however, to 



Jickeli's second paper on ** Der Ban der Hydroidpolypen." wliich 



•contains a careful study of C. calicuUita , I find the remaik " Der 



Raum zwisehen Hypostom und Armen ist hier so reducirt das auf 



Langsschnitten die Wandung des ersteren nui- wie eine Abzwci'^'ung 



<ler letzteren ersclieint." This might seem to imply merely a close 



approximation between the hypostome and the tentacles; the tiuure 



of a longitudinal stction shows dislinctly, liowi-ver, the mes(>sarc of 



the proboscis springing directly from that of the tentacles, and 



