261 PKOF. ALLMAN ON NEW GENERA 



alga. In every instance the gonangia presented a collapsed ap- 

 pearance, with wide longitudinal depressions (mostly three) sepa- 

 rated from one another by narrow longitudinal ridges. This 

 condition was not obliterated by boiling in water or in a solution 

 of caustic potash ; but it is possible that it does not exist in the 

 living Hydroid. 



Sebttjlakia. 

 Sertulakia arctica. Plate XIV. figs. 1, 2. 



Trojpliosome. Hydrocauliis attaining a height of about 1^ inch, 

 main stem undivided, slightly zigzag, sending off pinnately 

 disposed alternate ramuli, each internode of the ramuli car- 

 rying, near its middle, a pair of opposite, or nearly opposite, 

 hydrothecse. Hydrothecee elongated, free, and divergent from 

 the internode for rather more than their distal half, narrow- 

 ing towards the aperture ; aperture cleft, so as to present two 

 broad lateral teeth, to the lower angle between which is attached 

 a valve-like operculum. 



Gonosome. Gonangium springing from the internode, just below 

 the base of a hydrotheca, elongate-ovate, with a constriction a 

 little beyond its middle, terminating distally in a rather wide 

 tubular outlet. 



Locality. Spitzbergen, Mr. JEaton. 



This is an elegant and delicate little species. It is difficult to 

 determine the exact form of the hydrothecal orifice, the walls 

 being here very thin and collapsible. In most of the hydrothecse 

 the appearance of an impei'fect diaphragm could be seen at some 

 distance within the orifice. 



Desmosctphus, nov. gen. 



TropJiosome. Hydrocaulus jointed, each internode corresponding 

 to one or more pairs of hydrothecae. Hydrothecse adnate to one 

 another in pairs, and each pair adnate to the front of the hydro- 

 caulus. 



Gonosome. Gonangia simple, borne along the front of the hydro- 

 caulus. 



The genus Desmoscyphus resembles TTiuiaria in its hydrothecse 

 being adnate to the hydrocaulus ; but it differs from it in the fact 

 of its hydrothecse being also adnate to one another in pairs, which 

 are thus all brought to one side of the hydrocaulus, and in the 

 further fact of certain parts of its hydrocaulus being divided into 



