Simpson — A Revision of the GorgoneUidae. 263 



canals mnch larger than tlic others, and, no matter at what level the 

 section be taken, this number is constant for the specimen (see figs. 

 80, 13, 19, 24, and 111). There is only one exception to this rule, namely, 

 Scirpearia pcctinrda (fig. 43«) ; but in this case the conditions which 

 occasion it are themselves exceptional, and will be described later. In 

 the polyp-bearing branches the rule, however, holds good (fig. 436 and c). 

 In the great majority of cases the typical number is two — e.g. J. juncca, 

 J. gcmraacca ; but in two colonies examined, viz., Jvncdla triUncata (Thomson 

 and Henderson), and Sciipearia quadrilineatu n. sp., there is a departure. 

 In the former there are tliree and in the latter four (see figs. 25 and 111). 

 These large main longitudinal canals are always symmetrically arranged, 

 either 



(1) diametrically opposite (two) (fig. 10), or 



(2) at the ends of radii enclosing equal angles (three) (fig. 25), or 



(3) at the ends of two diameters at right angles to one another (four) 



(fig. 111). 



(h) They exert an influence on the extenud form of the eolony: — (1) A very 

 characteristic feature of Juncellids is the fact that in nearly every colony 

 examined there is a certain number of longitudinal tracts devoid of polj'ps. 

 This may be very marked, as in the case of Scirpearia flxigellum, 

 Scirpearia ceylonensis, and Juncclla ramosa, or less marked in, e.g., Scirpearia 

 vcrmcosa. In all these the number is always tivo. 



In Juncclla trilvncata, however, the number is three, and in Sdiyearia 

 quculrilineata the number is four. 



(2) These longitudinal bare tracts are symmetrically disposed, and 

 correspond in position to the internal large main canals. The presence 

 therefore of a certain number of bare tracts, and the consequent grouping of 

 the verrucae into a corresponding number of longitudinal series, are thus the 

 outward manifestation of the internal structure as expressed in the inner 

 series of longitudinal canals. These bare tracts are sometimes marked by a 

 longitudinal ridge or depression ; but this is due to the large canal being 

 either distended or in a collapsed state. 



Since this phenomenon is a constant for any individual specimen, 

 it seems to us that it may with safety be considered of taxonomic 

 importance. 



(c) Tliey produce an effect on the surface of the axis. — "The surface is 

 marked by longitudinal striae " ; " Eidges and furrows occur on the surface 

 of the axis " ; such statements enter into the description of a great number of 

 specimens given by various authors. A close examination of a transveree 



K.l.A. PliOC, vol.. XXYUI., SECT. 11. [^ ^] 



