NOTE ON A NEW BRITISH ECHIUROID GEPHYREAN. 373 



do not, so far as I can determine, ever branch again. They 

 are very long, and are closely intertwined in their proximal 

 parts (see figs. 19 — 21), so as to be difficult to follow ; 

 but all those I have teased out seem, like the one shown in 

 fig. 22, to be free from the neighbouring twigs. The appear- 

 ance of repeated branching seen in figs. 19 and 20 is due to 

 frequent crossing of the twigs. This is a case, then, of what 

 Rietsch^ calls a simple ramification, in distinction from both 

 the unbrauched tube of some other species of Thalassema^ 

 (e.g. T. Neptuni) and the doubly ramified organ of Bo- 

 nellia viridis. Rietsch figures and describes the posterior 

 nephridium of Bonellia minor as being simply ramified, but 

 the twigs in that case are not nearly so long nor so numerous 

 as in the present species. In anatomical condition, then, so 

 far as this organ is concerned, the present form lies between 

 Bonellia viridis and B. minor, and is certainly in this one 

 character more like that genus than like the typical Thalas- 

 sema. The posterior nephridia of Hamingia arctica seem, 

 from the figures and description of Danielssen and Koren,^ to 

 resemble very closely our form. 



Each of the milk-white twigs bears a little bell-shaped funnel 

 or nephrostome at its distal end (figs. 21 and 23). The margin 

 of the funnel has a thickened ciliated rim (fig. 24). This 

 arrangement is very like that of Bonellia minor as figured 

 by Rietsch. The further details of appearance are sufficiently 

 shown by my figures (PI. 28, figs. 19 — 24). The nephrostomes, 

 then, are very numerous, and open freely by wide ciliated 

 mouths into the body-cavity. 



Anterior Nephridia. — These also are a single pair. 

 They lie one at each side of the alimentary canal ventrally, in 

 the anterior one fourth or so of the body (figs. 7, 8, 25, 7i). 

 They are large, and in both my specimens are distended with 



1 ' Recueil Zool. Suisse,' t. iii, 1886. 



- T. gigas has nephridia which, from Miiller's figure, seem to resemble 

 those of our form. 



J ' Gephyrea of Norwegian North Atlantic Expedition, 1876-8,' Chris- 

 tianifl, 1881. 



