Simpson — A Revision of the Gorgonellidae. 13 



V. — Macroscopic and Microscopic Characters as a Basis of 



Classification. 



(1) coenenchyma. 



(a) Surface. — The surface of the coenenchyma is generally smooth to the 

 naked eye, but presents a glistening, arenaceous appearance when viewed 

 with a lens. This is due to the small spicules, which project slightly, eitlier 

 singly or in. small clusters. 



Thickness. — The thickness varies in different species; e.g., in Junccllci 

 juncea,^ Juncella gemmacea, and Scirpearia furcata it is usually thick ; but in 

 Juncella racemosa, Sdrpearia alba, and Scirpearia flagellum it is generally 

 thin. 



On the other hand, however, extremes may be found in ditterent speci- 

 mens of the same species. No better example of this can be cited than 

 Juncella juncea (see later). For this reason the thickness of the coenen- 

 chyma cannot Ije regarded as a specific criterion. It does, liowever, affect 

 the general appearance of the colony, inasmuch as the verrucae are capable 

 of greater retraction in those .specimens in which the coenenchyma is above 

 the average thickness. (See figs. 9 and 10 (a, b, and c) of Juncella jmicea, 

 fig. 100 of Scirpearia aiulaiiiancmis, and figs. 83 and 88 of Scirpearia furcata.) 

 As a contrast to these, figs. 49 and 56 of Scirpearia Jlagcllum may be taken 

 as typical. One very important feature in regard to the thickness of the 

 coenenchyma is the fact that this is almost a constant in any one specimen ; 

 the difference in the thickness of the colony is really due to the axis. 



It, therefore, follows that, although the thickness of the coenenchyma 

 varies very little in any individual specimen, it may vary considerably in 

 different specimens of the same species, and is therefore of little if any 

 taxonomic value. 



Coiisidency. — The coenenchyma is densely packed with minute spicules, 

 and is consequently very granular and brittle, especially when dry. It 

 presents a gritty, uneven surface when cut with a knife. 



(6) Eistology. — The coenenchyma is divided into an outer non-canal- 

 bearing part in which the polyps are embedded, and an inner part in wliich 

 small canals ramify in all directions (figs. 10 and 19). Tiiese are separated 

 by a series of longitudinal canals, which are arranged peripherally. The 

 proportionate thickness of these two parts varies greatly in different 

 specimens, and is of no taxonomic value. 



' Tlie generic and specific names given in this p»rt of the memoir are tli"«" ulii. li mi' ailnpti'il in 

 the final classification (q.v ). 



