100 MR. E. S. RUSSELL ON A NEW HYDROID. [Feb. 6, 



at opening of umbrella-cavity. Exumbrella with a few nemato- 

 cysts scattered over it. "Velum well developed. 



Manubrium, when extended, as long as umbrella- cavity, 

 cylindrical, and with narrowed end. 



Mouth simple, circular, with a ring of bead-like nematocysts 

 closely surrounding it. 



Four ocellar bulbs, ellipsoid : one of these is somewhat larger 

 than the others. Radial canals four, simple. 



Dimensions. Length of bell 0"8 mm.; breadth of bell 0-7 mm. 



Colours. Manubrium tinged with yellow, but ver}^ faintly. 

 Ocellar bulbs golden yellow. 



The type specimen of TrichorJiiza hrimnea was discovered on 

 June 29th, 1905, clinging to the tentacles of a specimen of 

 Corymorpha motans Sars, dredged in 17 fath. at Ettrick Bay, Bute, 

 Firth of Clyde. The filiform hydrorhiza with its branches was 

 intertwined among the tentacles of the Gorym,orpha so as to be with 

 difliculty unravelled from them. The Trichorhiza was kept alive 

 for a day or two at the Millport Marine Biological Station, and 

 gave off on July 1st the medusoid which has been descr'ibed. 

 It was usually to be seen half -retracted into its protective cup, 

 with the proximal tentacles much contracted, and the distal ones 

 looking like mere knobs. On the rare occasions on which it was 

 observed in an expanded condition, the tentacles of the outer 

 circle were seen to be held rather stiffly extended. 



Systematic. On account of its possession of two verticils of 

 tentacles, the proximal filiform and the distal capitate, Trichorhiza 

 is to be referred to the family Pennaridse as constituted by 

 Allman (1). That family contained the following genera : — 

 Pennaria Goldfuss, Halocordyle Allman, S'tauriditim Dujardin, 

 Vorticlava Alder, Heterostephanus Allman, Acharadria Wright, 

 and Acaulis Stimpson. 



Two other genera have sometimes been associated with the 

 Pennarid?e, namely Blastothela Yerrill, which is placed among the 

 Pennaridee by Delage et Herouard (3), and Tiarella Schulze, which 

 is referred to the same family by G. Herbert Fowler (4). But such 

 an assemblage of genera by no means makes up a homogeneous 

 family. K. 0. Schneider (6), in his critical revision of the 

 classification of Hydroids, has removed Staiiridium to his amended 

 family of the Oorynidje. Tiarella^ with its three rows of capitate 

 tentacles, has also been refeixed to this extended family of the 

 Oorynidse by Mme. Motz-Kossowska (5), who follows Schneider's 

 classification in the main. These two genera are rightly separated 

 from the other genera of Pennaridse, as they have little in common 

 with the Pennarian type. The seven which remain of the nine 

 genera mentioned above are all fairly closely allied to one another. 

 Halocordyle certainly must be united with Pennaria, and we may 

 with Schneider also bring under Pennaria the genera Vot^ticlava, 

 Acharadria, Acaulis, and Heterostephanus. Heterostephamis is 

 allied by its medusoid with the Corymorpha type. Blastothela too 



