82 SIDNEY r. HARMER. 



specific characters are not completely shown in the immature 

 condition of this structure. There are occasional cases in 

 which the ooeciostome of a given colony may appear inter- 

 mediate between two species. In most of these cases com- 

 parison with other specimens will, however, usually leave no 

 doubt of the existence of a definite character for the ooeciostome 

 of each species, in spite of the occasional occurrence of difficult 

 cases. 



The value of the characters of the ooeciostome in diagnosing 

 a species is strikingly illustrated by the specimens of T. 

 flabellaris, Fabr., which have come into my hands. Fig. 4 

 is an Arctic specimen of this species, dredged by Colonel H. W. 

 Feilden on July 1st, 1895, in Barents Sea, and presented by 

 him to the Cambridge Museum of Zoology. Although the 

 colony is very much smaller than the form of this species 

 figured by Smitt (40, pi. ix, fig. 6), it possesses no less than six 

 complete ovicells, each with a fully formed ooeciostome (1 — 6), 

 five of which are visible in the position in which the colony 

 lies, besides one immature ovicell (7). The ovicells are 

 crowded and are very small, exhibiting hardly any of the 

 lobing which may occur in this species as in others. The 

 principal characteristic of the species, the flattened shape of 

 the ooeciostome, is nevertheless as well marked in each ovicell 

 as it is in the lobed ovicells of a larger colony, sent to me by 

 Dr. Nordgaard from Hammerfest. 



The above case can hardly be regarded as a mere individual 

 abnormality. I have examined four specimens (including the 

 above) from Colonel Feildeu's collection, and all of them 

 showed the same peculiarities. Two other colonies (about the 

 same size as the above) had each four small, contiguous ovi- 

 cells with fully formed ooeciostomes, and an immature fifth 

 ovicell. The last consisted (unlike the others) of two diverg- 

 ing lobes, which may, however, have been formed from two 

 larvae. One lobe had two ovicells with ooeciostomes, and at 

 least one immature ovicell, and the other lobe had one ovicell 

 with a fully developed ooeciostome. In every ovicell the long 

 flattened ooeciostome, which I regard as the distinguishing 



