254 CORDYLOPHORA ALBICOLA. 



this mollusc is now making its way into our canals and rivers. It is a light-shunning animal 

 delighting in such obscure places as the under side of a large log of floating timber, and always 

 avoiding exposure to the direct rays of the sun. The specimens already mentioned as flourishing 

 in water supplied for domestic purposes to the inhabitants of London were found in a dark 

 cistern constructed in the interior of a house, and totally excluded from all access of daylight. 



The hydranths of Cordijlophora lacustris are very mutable in shape, aud they may be seen, 

 according to their state of contraction, varying from a short fusiform or clavate figure to a nearly 

 cylindrical one. The tentacles when contracted are short and thick, but may be extended to 

 long thin thread-like appendages, which float listlessly in the water, as they yield to every 

 impulse of the passing current. 



The gonophores afford a good example of that form in which the spadix becomes branched, 

 enveloping in its ramifications the ova or the spermatozoa. This branched condition of the 

 spadix I mistook at first for a system of radiating canals,' an error which subsequent observations, 

 aided by experience in the investigation of other hydroids, have enabled me to correct. 



Dr. F. E. Schidze has recently made this species the subject of an excellent memoir, in which 

 he discusses many important points bearing in the minute structure of the Hydroida. (See 

 above. Part I, p. 228.) 



*^* 2. CoRDTLOPHORA ALBICOLA, Kirchenpauer. 



CoRDYLOPHoiiA ALBICOLA, — Kifchenpaiier. la a letter to Mr. Busk in Journ. Mic. Sci., 1861, 



p. 283, pi. ix, figs. 12—14. 



TROPHOSOME. — Htdrocaultjs attaining about one inch in height ; branches 

 alternate, annulated ; perisarc terminating abruptly below the hydranth. 



GONOSOME not known. 



Hahiiaf. — On buoys in tidal rivers near the highest limit of the tide. 

 Locality. — The River Elbe, Senator Kirchenpauer. 



I have selected the charactei's given in the above diagnosis from Senator Kirchenpauer's 

 description and figures communicated by Mr. Busk to the ' Journal of Microscopic Science.' 

 Kirchenpauer believes that in the form of the body and tentacles of the hydranth characters may 

 also be found by which Cordyloplwra albicola shows itself to be a distinct species from 

 Cordylophora lacustris ; in these, however, I can see nothing beyond indications of a particular 

 state of contraction. It is in the well-marked annulation of the branches, not merely at their 

 origin but throughout, and in the abrupt termination of the chitinous perisarcal tube as shown 

 in Kirchenpauer's figure, that the only valid grounds of specific distinction are to be found. 



The species was discovered by Senator Kirchenpauer on those buoys in the estuary of the 

 Elbe, which lie farthest from the upper limit of the tide, and consequently most removed from 



' ' Phil. Traus.,' loc. cit. 



