364 Prof. 0. C. Nutting on 



Linn., trom which it differs in having a much shorter pedicel, 

 a not strictly tubular hydrotheca, a greater number of segments 

 to the operculum, in the absence of the tubular extension of 

 the operculum, and in a much thinner structure, the hydro- 

 theese being of glassy transparency in 0. hispida, but of a 

 decided brownish or yellowish horn- colour in G. syringa. 

 The most striking feature, however, of the present species is 

 the remarkably hispid appearance of the tentacles, which 

 appear to be made up of a series of triangular segments, on 

 account of the formidable array of large nematocysts with 

 which they are armed. Whilst examining the expanded 

 tentacles with a -§ objective I was so fortunate as to see these 

 batteries of projectiles suddenly explode, sending out a perfect 

 maze of barbed threads, which appeared to be larger and 

 longer than those of any hydroid that I have seen except 

 N ematophorus grandis, Clarke. 



In the absence of the gonosome it is impossible to say with 

 any certainty to which genus this interesting little species 

 belongs. The general form of the hydrotheca, the cylindrical 

 hydranth with conical proboscis, together with the convergent 

 teeth, give a facies like tliat of the genus Opercularella^ in 

 which it is provisionally placed. 



Plumularia Alieni^, sp. n. (PI. XV. tigs. 1-6.) 



Trophosome.- — Colony attaining a height of ^ to | inch. 

 Stem simple, monosiphonic, divided into regular internodes, 

 each of which bears a hydrocladium on a process springing 

 from near its distal end. Hydrocladia divided into altei'- 

 iiating hydrothecate and intervening internodes, the former 

 being the longer, with deep annulations occasionally appear- 

 ing near the nodes. Hydrotheca rather shallow, cup-shaped, 

 borne near the distal ends of the internodes. Nematophores 

 small, bithalamic ; a supracalycine pair reaching just above 

 the top of the hydrotheca, a mesial nematophore some distance 

 below the hydrotheca, and another in the middle of each 

 intervening internode ; a pair of cauline nematophores in the 

 axil of each hydrocladium and one just below the middle of 

 each cauline internode on the side opposite the hydrocladium 

 borne by that internode. Hydrothecge with about 16 ten- 

 tacles and a conical proboscis. 



Gonosome. — Gonangia borne singly at the bases of the 

 hydrocladia, of two kinds, one (female ?) obconic, curved like 

 a horn, narrowing rapidly to the very short pedicel. In 



* Named after the Director of the Plymouth Laboratory, an enthusi- 

 astic worker in marine zoology. 



