AND SPECIES or HTDROIDA. 255 



general lamination, consist of two distinct layers. The external 

 one, itself distinctly laminated, forms a sort of sheath which in- 

 vests the inner one, also laminated, and can be separated from it 

 by the needle. The tubular cavity of the spine, which is con- 

 tinuous from its summit to its base, is filled with coenosarc. 



The description here given is that of a female colony, no male 

 specimen being contained in the collection. 



The colony covered the surface of a gasteropodous shell, 

 Trophon clathratum, Linn., which was obtained oiF the coast of 

 Spitzbergen, and is still inhabited by the moUusk. Its high 

 northern locality thus gives to Hydractinia monocarpa a special 

 interest from a distributional point of view. 



POnOCOBYNID^. 



PODOCOKTNE. 



PoDOCORYNE iNEBMis. Plate X. figS. 4, 5. 



TropTiosome. Hydrorhizal expansion forming a thin layer en- 

 tirely destitute of projecting chitinous spines. Proliferous hy- 

 dranths but slightly smaller than the sterile hydranths. 



Gonosome. Gonophores forming a verticillate cluster at a short 

 distance below the tentacles. 



Localities. Oeresund and Middelfartsund, Denmark, Zool. Mus. 

 Cop. 



The present species comes very near to Podocoryne carnea, and 

 may possibly be only a varietal modification of it. It differs from 

 it, however, in the entire absence of the chitinous spines which 

 in P. carnea are developed from the hydrorhizal expansion, as 

 well as in the much less arrested condition of the proliferous hy- 

 dranths. It is possible that specific characters may be afforded 

 by the free planoblasts ; but the exact form of these can be deter- 

 mined only from living specimens. 



The specimens occur on the shells of young living individuals 

 of Nassa reticulata. 



CLAD COP TNID^. 



Cladocoktne. 



Cladocobyne pelagica. Plate X. figs. 6, 7 . 



Trophosome. Hydrocaulus attaining a height of about one fifth 

 of an inch, simple, with the perisarc distinctly annulated towards 

 the base. 



