HYDROIDA II 



177 



the blastostyle is shaped rather like a cluster of grapes, the outermost swellings, shown in the figure, 

 consist each of a compact accumulation of incipient gonophores. Nematocyst-bearing terminal buds 

 appear to be altogether lacking. The size of the blastostyles decreases nearest the ventral interval, 

 whence a new formation evidently takes place. 



With regard to the anatomical character of the polyp, we must notice the large mesentery 

 which divides the gastral cavity into an upper (oral) and a lower (basal) section; it has a large median 

 opening. The radial canals have a large lumen; they do not appear to divide, and alternate with the 

 tentacles, and thus do not stand in open connection with the latter; their number corresponds to that 

 of the proximal tentacles. — The blastostyles are hollow, and communicate openly with the interior 

 of the polyp, but it was impossible to determine exactly whether their communication with the gastral 

 cavity is direct, or proceeding indirectly through the radial channel. 



Material: 



"Ingolf" St. 28 65°i4' N., 55°42' W., depth 420 fathoms, 3,2°. 



The only specimen procured presents the following features: Total length 120 mm., of which iiomm. 

 fall to the hydrocaulus. Distal diameter of the stalk 3 mm., close above the root hairs the transverse section 

 is 7 mm. The polyp disc has a total breadth of 12 mm. and a length of 9 mm., measured from the 

 bottom of the ventral incision. There are 85 proximal tentacles; the longest of those intact is 55 mm. 

 The distal tentacles are very closely set, often displaced, giving a slight indication of three rows; 

 there are between 80 and 90 oral tentacles of up to 5 mm. length. The blastostyles are closely packed 

 together, and form three indistinct rows, the longest is 4 mm.; there are between 70 and 80 in all. 



On comparing the present specimen with the species of Branchiocerianthus previously described, 

 we find several points of difference, albeit none very striking in itself. The peculiar kidney-shaped 

 appearance of the disc (PL I, figs. 2 and 3), as also the curled margin of the oral aperture, would 

 seem to be different from the species previously described, and has led me to regard the specimen for 

 the present as representing a distinct species, Branchiocerianthus reniformis. The lack of terminal 

 buds bearing nematocysts in the blastostyles brings the species near to Branchiocerianthus n. sp. Stechow, 

 (1913 p. 54I from which, however, it is immediately distinguished by its undivided radial canals. The 

 habitus of the hydranth distinguishes it from Branchiocerianthus urceolus Mark; this may, however, 

 possibly be taken as due to a difference in the state of contraction. From Branchioceriantlius impe- 

 rator (Allman) again, the species differs in the lack of nettle buds on the blastostyles. From the appe- 

 arance of the specimen in 1904, Branchiocerianthus reniformis has also a different colour; the body of 

 the polyp was then white, the blastostyles being a deep violet blue; now, after having lain many 

 years in alcohol, it is an even grey. 



The individual can hardly be fully grown, and corresponds in point of size only with the 

 smaller specimens of Branchiocerianthus urceolus found. The number of proximal tentacles agrees 

 mainly with that in this species, but there are far fewer distal tentacles; save for one of Allman's 

 specimens of Branchiocerianthus imperator (1888) all the other individuals found belonging to this 

 genus had considerably more distal tentacles. The number of blastostyles takes up an intermediate 

 place between the two mentioned species, and is somewhat lower than in Branchiocerianthus n. sp. 



The Ingolf-Expedition. V. 7. 23 



■» V 



