HYDR01DA. — HALE, 5 



Family SERTULARIID^. 



GrENUS SvNTHECIUM, All man. 



Stnthecium subventricosum, sp. nov. 



(Plate i„ tigs. 3—5.) 



Hydrophyton usually under one inch in height, monosiplionic, 

 pinnate, many of the pinnae anastomosing with other parts of 

 the polypidom or continued into stolons ; stem-internodes (except 

 at the base) long, each usually bearing a pair of opposite 

 hydrotheca? at its base and summit, with a pair of opposite 

 pinna? in the middle; those at the base short, bearing a pair of 

 opposite hydrotheca? only. Pinna? divided into stout internodes, 

 each supporting a pair of hydrotheca? ; the first hydrotheca on 

 the proximal side of each pinna much higher than its fellow, 

 those on successive internodes less uneven, till at about the third 

 to the fifth internode they become opposite, 



Hydrotheca? tubular, stout, lower part vertical and often 

 somewhat ventricose, distal part curved outward, free part short, 

 aperture circular, margin a little sinuated at the sides and very 

 slightly everted, looking upwai'ds and outwards, 



Gonotheca? small, nearly globular, with five to six transverse 

 ridges interrupted in the middle on opposite sides, mouth 

 prominent, conical, aperture small. 



Polypidom thin, colourless and transparent, more or less tangled 

 owing to the anastomosing of the pinna 1 . 



This species is allied to 8. patulum, from which it may readily 

 be distinguished by the larger, and especially the stouter, 

 hydrotheca?, with their tendency to a ventricose condition, and 

 the distinctly sub-alternate arrangement of those on the proximal 

 parts of the pinna 1 . In S. patulum it is not unusual for the fir.st 

 hydrotheca on the proximal side of each pinna to be set a little 

 higher than its opposite neighbour ; here, however, the irregularity 

 is much more pronounced. Each successive pair comes nearer 

 to a strictly opposite condition, which is sometimes attained by 

 the third pair, sometimes only by the fourth or fifth. Even after 

 this however irregularities are not uncommon, and in some 

 cases the more distal pairs deviate from the normal arrangement 

 in the contrary direction to the proximal. 



In comparing my specimens of S. subventricosum, S. patulum, 

 and S. orthogonium, I find differences in the prevailing arrange- 

 ment of'the internodes in all three. 8. patuhim generally has 

 from one to three short proximal internodes, each of which 

 supports a single pair of hydrotheca" ; above these the internodes 

 are long, and each bears a pair of pinnae close to the summit, 

 with a pair of hydrotheca? about the middle. 8. orthogonium 



