814 MR. J. RITCHIE OX HYDROiDS [May 24, 



its hydrothecfe and some of the varieties of the latter species 

 (see Broch, 1909 b, text-fig. 22). It approache.s most closely 

 C. nuttingi Hargitt (1909, p. 378), fi-om which it difl'ers in being 

 smaller in size, in being cylindrical instead of tapering from 

 hj'drothecal margin .to base, and in lacking distinctly annulated 

 peduncles, with "annulations occasionally extending some distance 

 (rarely over the entire body) on the thecal walls." 



I regard the unnamed specimen, mentioned and figured by 

 Miss Thornely (1908, p. 83, pi. ix. fig. 5), from Khor Shinab, 10 

 to 12 fathoms, in the Soudanese Red Sea, as belonging to this 

 species. 



CuspiDELLA cosTATA Hincks, 1868. (Plate LXXYII. iig. 8.) 



To the short and incomplete description given by Hincks the 

 following observations may be added. The hydrotheca is cylindri- 

 cal for the greater part of its length, but near the base it gradually 

 tapers downwards. Frequently the basal portion of the hj-dro- 

 theca lies along the object upon which the epizoon is growing, 

 the distal portion bending upwards at an angle, slightly after the 

 manner of Lafo'ea serrata. Within the bent portion the retracted 

 polyp is generally found. Similar bent hj-drotheca; have been 

 described by Dr. Billard from La Hougue (1904, p. 165). 



The lines of growth held to be characteristic of the species, 

 and clearly marked in our specimens, are not lines of growth in 

 the ordinary sense, marking the place where new gi-owth has 

 commenced. They indicate, instead, the margins of earlier hydro- 

 thecie, the opercular flaps of which occasionally remain attached 

 and give an appearance of longitudinal fluting to the succeeding 

 portion of the hydrotheca, as is suggested in the terminal seg- 

 ment in Hincks's figures (1868, pi. xl. figs. 5, 5 a). The secondary 

 hydrotheca (produced probably on the regeneration of an entirely 

 new hydr'anth) lies within the primary, and for some distance 

 their walls, though in close contact, remain distinct. The tertiary, 

 when such occurs, lies within the secondary, and so on. Thus 

 the terminal segment is, as Hincks observes, " of thinner material 

 than the rest," for its walls are those of a single hydrotheca, 

 while proximal to the uppermost segment the walls, owing to the 

 telescoping arrangement, are considerably strengthened. It is 

 noteworthy that the proxim.al segment is usually of distinctly 

 less calibre than its successors. The operculum of the hj'drotheca 

 is composed of about 14 or 15 flaps. 



The h3'di'anth is strongly retractile, retiring on contraction to 

 the proximal third of the hydrotheca. It appears to have about 

 six to eight tentacles, which are closely set with whorls of large 

 oval nematocysts, the whorls being 7-5 jj. apart. The average 

 size of the nematocysts in these whorls is 5-2 p. long by 2 /n 

 bi'oad, but at the tip of the tentacle larger examples occui-, 10-5 /i 

 long by 5 //. broad. 



Ko gonosome was observed. 

 [16] 



