PENNATULIDA. 



8l 



After the comprehensive description which Danielssen has given of this species, on the basis 

 of the excellent material of the North-Atlantic Expedition, its identification will generally be an easy 

 task, and the principal features of its structure be ascertained. There are, however, several places 

 where additions or alterations have had to be made; in the above short description some of these 

 have already been mentioned, and in the following they will be more particularly discussed. Thus, it 

 may be pointed out that Umbellida encriiiits like the preceding species (and probably most Umbelliila- 

 species), is provided with zooids on the whole stalk from its very earliest stage, at all events in all the 

 stages hitherto known. Danielssen says indeed, 1. c. p. 52, that zooids occur everywhere on the stalk 

 with exception of the inferior part of the bulbous portion , but by this he has evidently been thinking 

 of the large , full-grown specimens, as none of his figures of young stages show zooids on the stalk 

 much below the cluster; only in fig. 20, PI. VII zooids seem to be indicated down the thin part of the 

 stalk, and in the text it is for the first time mentioned in the detailed description of this specimen 

 (Nr. 5, 380™", with thirteen developed polyps in the cluster) that zooids are generally found .further 

 down the stem, they become still more dispersed, and are situated, parti)", in a series on each side> 

 (I.e. p. 23); in four of the large specimens later described, zooids on the stalk are especially mentioned, 

 most thoroughly for Nr. 12. A very minute examination shows, however, as before mentioned, that 

 they are found in the very youngest stages, which I have been convinced of by inspecting Danielssen's 

 material. My two young stages mentioned above (Nr. i and 2 of the table) with respectively four and 

 seven polyps in the cluster carry zooids all along the stalk to the bulbous part; these zooids are 

 very small, much smaller than those placed near the cluster which feature is preserved also in 

 the older colonies, where the number becomes very large; the>- certainly do not seem to have an_\- 

 tentacle; I have succeeded, however, in seeing such a tentacle in a single specimen (Nr. 10), in zooids 

 placed below the sheath-formed upper dilation . In the youngest stages these zooids of the stalk are 

 placed regularly in two longitudinal stripes, so that the dorsal and ventral sides of the stalk are naked; 

 this latter fact, however, is only to be decided with difficulty on account of the spiral-like twisting 

 of the stalk; frequently, individuals a little larger alternate with quite small ones; the latter have 

 evidently just appeared. By and by, as the colony grows, the number of zooids in the stalk increases 

 greatly; in large specimens, as Nrs. 3 and 4 of the table, they are arranged in short longitudinal rows, 



The In^olf-Expedition. V. 1. il 



