I0 8 HYDROIDA II 



drothecse expanding distally (Eudiphasiri) from those in which the hydrothecse are bottle-shaped (Abie- 

 tinarici). There are, however, transition forms, and the great variation in the hydrothecae in most spe- 

 cies renders a limit such as that so drawn extremely vague. 



We now find, however, that the structure of the polyp is different in the two groups, the blind 

 sack being only in the latter found in full development. This is an organisational feature of so con- 

 siderable importance as not only to warrant, but even to demand, a generic distinction between the 

 two groups, which also on the whole present interesting points of difference in the gonangia. In 

 Diphasia, we find that the female gonothecse are as a rule furnished with spinous or leaf-shaped out- 

 growths, which very often fold in together, forming a distal chamber for the brood, a marsupium. 

 This is a biological phenomenon, and from a phylogenetic point of view of less importance; on the 

 other hand, it is interesting to note that it here appears to occur as a constant characteristic in a 

 whole series of related species. It is also worth noting that this feature is likewise found in Sertula- 

 rella tamarisca (Linne) a species which appears to form a link between Scrtularella and Diphasia. 



Diphasia fallax (Johnston) Al. Agassiz. 



1847 Sertularia fallax, Johnston, A History of the British Zoophytes, p. 73, pi. n, figs. 2, 5, 6. 

 1865 Diphasia fallax, Al. Agassiz, Illustrated Catalogue, p. 142. 



Upright pinnate colonies with more or less pronounced monosiphonic main stem, and as a rule 

 with convex foreside. Stem and branches are divided into internodia, each bearing a pair of oppos- 

 itely placed hydrothecse. The branches proceed alternately from the stem, and are themselves often 

 sparsely branched, frequently with tendril-like terminal parts. Between two successive branches on 

 the same side of the stem there are two to four hydrothecse, the one of them being at the corner of 

 the branch. The hydrothecse are deeply embedded, with a free distal part of the adcaiiline wall, in 

 length equal to the opening diameter, or slightly less. The aperture is round, the margin with ad- 

 cauline sinus, in which the large opercular plate is attached. The greatest diameter of the hydrotheca 

 is at the opening. 



The gonothecse are situate on the upper side of the branch or on the fore side of the colony. 

 The males are pear-shaped, with four distal short broad spines, and a short conical to cylindrical cen- 

 tral neck. In the females, the four spines have developed into four broad triangular blades, which 

 close in together over a distal brood-chamber in which the larval development takes place. 

 Material : 



"Ingolf St. 3, 6335' N., io24' W., depth 272 fathoms 0,5. Variety. 

 51, 6 4 i4' N., i 4 22' W., 68 7,32 



- 87, 6 5 02, 3 ' N., 2 3 5 6,2' W., no 



93, 6 4 2 4 ' N, 35 t 4 ' W, 767 1,46 



94, 6 4 5 6' N, 3 6i 9 ' W, 204 4 ,i c 



95, 6 5 i 4 ' N., 3 o 39 ' W., 752 2,i c 



96, 6 5 24' N., 2 9 oo' W., 735 1,2 



- 98, 6 5 3 8' N, 2 6 C 2 7 ' W., 138 5,9 



- 115, 7050' N., 829 r W., 86 0,1 



-0 



