278 SERTULAttHD^E. 



waved, compressed, annulated at the bottom, pinnate 

 above, generally naked below; pinna usually simple, 

 sometimes much divided and subdivided dichotoniously, 

 alternate or subalternate, attenuated at the base, approxi- 

 mate ; HYDROTHECJE subalternate, closely set, broad and 

 truncate below, becoming narrower above and projecting 

 slightly, with a plain, circular orifice ; GONOTHEC.E pear- 

 shaped, smooth, with a round aperture at the top and 

 an operculum. 



ARTICULATA usually attains a height of from 4 to 

 6 inches. A very luxuriant specimen, dredged by Mr. 

 Hyndman off Sana Island (in forty fathoms), measured 

 10^ inches ; but this is quite an exceptional size. The 

 shoots are plumous in form, and, when living, of a "pellucid 

 amber-colour." They are commonly branched ; but there 

 is no regularity in the mode of growth. The pinnse are 

 usually alternate, but in some cases nearly opposite; 

 they are articulated, as in T. thuja, near the base to a 

 short projection from the stem, but are not deciduous to 

 the same extent as in that species. A row of calycles runs 

 up each side of the stem, two or three being placed between 

 every pair of pinnse. 



A remarkable variety occurs in Shetland, of which I 

 have a specimen from Mr. Norman, which has the pinnse 

 much slenderer than in the common form, and the caly- 

 cles somewhat widely separated (Plate LX. fig. d). The 

 habit, too, is diffuse, and some of the pinnse are much 

 ramified. 



Hab. Widely distributed, but not generally abundant; 

 on stones and shells from deep water. Cornwall, deep 

 water (50 fath.) (Couch): Devon, not uncommon (T. H.): 

 Scarborough (W. Bean): Northumberland (J. A.): Clyde 

 (Forbes): Norfolk, Peterhead, and Wick (C. W. P.): Sana 

 Island (Scotland) (Hyndman): Shetland (A. M. N.): Isle 



