SERTUL ARIADNE. 469 



of its growth. When very young (a) the vesicle is pear-shaped, 

 with a rim round its greatest circumference, upon which are 

 eight small tubercles. Within the rim is a dome divided from 

 the apex into four segments. As it increases, the tubercles elon- 

 gate to laminar spines, which bend inwards (6). At this period 

 it may be seen that the interior of the vesicle is divided into two 

 chambers ; the lowermost, which contains the ovarian column 

 is of the shape of a sugar-loaf reversed. The upper chamber is 

 larger and dome-shaped, and both are separated by a valve or 

 septum marked with concentric circles. When the ovary is 

 perfected, two of the spines are erect, larger than the rest, and 

 have a notch or bracket upon the outer edges ; the others are 

 either folding upon one another, or stand erect. The ovary is 

 also seen to be fluted upon its eight sides. After the escape of 

 the ova, the segment of the dome and laminar spines are all 

 erect, and have a very crowded appearance : the long spines 

 break off, or all of them, till at last nothing may be left but an 

 eight-sided fluted reversed pyramid, with a level top. 



SERTULARIA PTJMILA a. robust ; on Laminaria, Orkney Isds. ft. 

 slender, cells distant ; on filamentous algae, Humber. 



SERTULARIA FALLAX thirty-five fms. Orkney Islands. Forty fms., 

 Buchanness, June 1846. The 

 immature vessels are quad- 

 rangular, with four small tu- 

 bercles upon the angles, and 

 a tubular papilla at the top ; 

 in fact you will find upon 

 the upper or lowest pinnse 

 of those I send you, ovaries 

 from which your Fig. 12 

 might have been taken. From 

 this circumstance I had sup- 

 posed that S. pinnaster had 

 been founded upon an unripe specimen of S. fallax, and such 

 may still be the case, but more anon. The general features 

 of the growth of the vesicle are like those of S. rosacea ; like 

 that species, the interior is divided into two chambers ; the 

 tubercles become ramillse, which at first fold over the dome- 

 shaped top, and afterwards become erect. The colour of this 

 species varies from hyaline to a light claret. 



