134 
Z. HYDROIDA. 
Sertularia. 
is a large specimen, from the Frith of Forth, in which they are re- 
markably zig-zag or kneed, so as to give it a peculiar character and 
appearance. In the same collection are specimens from the Cape of 
Good Hope, which differ in no respect from those of our shores. 
15. S. argentea, polypidom cauliferous ; cells nearly oppo- 
site or subalternate , urceolate , acutely pointed , the upper half di- 
varicated ; vesicles oval . Merret. 
Plate XII. and Plate XI. Fig. 3, 3. 
Corallina muscosa, alterna vice denticulata, ramulis in creberrima capilla- 
menta sparsis, Rail, Syn. i. 36, No. 17. Muscus marinus denticulatus 
minor ramulis in creberrima capillamenta sparsis, Pluknet , Phytog. tab. 
48, fig. 3 Muscus marinus minor denticulis alternis, Morris. Hist. 
Plant. Oxon. iii. 650, tab. 9, fig. 4 Squirrel’s-tail, Ellis, Corall. 6, 
No. 4, pi. 2, fig. c, C. Sertularia cupressina, $, Lin. Syst. 1308 
S. argentea, Ellis and Soland. Zooph. 38. Turt. Gmel. iv. 677. Wern. 
Mem. i. 564. Berk. Syn. i. 216. Turt. Brit. Faun. 213. Stew. Elem. 
ii. 442. Bose, Vers, iii. 108. Lam. Anim. s. Vert. ii. 117. Lamour. 
Cor. Flex. 192, Corall. 84. Hogg's Stockton, 32. Templeton in lib. 
cit. 468. Johnston in Trans. Newc. Soc. ii. 258, pi. xi. fig. 4 La 
S. argentee, Blainv. Actinol. 480 Dynamena argentea, Flem. Brit. 
Anim. 544. 
Hab. In deep water. On oysters and other large bivalved shells, 
as also on the stalk of Laminaria digitata, common. 
Polypidom from 6 to 18 inches high, cauliferous, the stem percur- 
rent, filiform, waved or straight, smooth, of a dark brown colour, di- 
vided at rather wide but regular intervals by an oblique joint, clothed 
with short panicled dichotomous branches which spread out on every 
side, and being all of the same size or nearly so, (excepting at the 
bottom where they are less branched and smaller, and at the top where 
they also frequently become gradually shortened,) the whole coralline 
assumes somewhat of the shape of a squirrel’s tail, and has given ori- 
gin to its English name. Two branches usually arise from each in- 
ternode of the stem, and they come off in such a manner that four 
or five of them complete a whorl. The polype-cells on the stem are 
alternate, appressed, and appear to be less than those on the branches, 
which are placed in two rows with their orifices inclined to one side ; 
they are bellied like a Florence-flask with a narrow divaricated neck 
terminated with a small oblique aperture : on some of the branchlets 
every pair is separated by a joint or stricture, while on others several 
pairs occur in succession without the interference of such a structure. 
Vesicles scattered, oval, smooth, attenuated at the base. 
In young specimens of an inch or two in height the polypidom is 
simply pinnate, and as it rises the branches gradually divide into more 
