20 EDWARD T. BROWNE. 



In the distal half of the umbrella the perradial and interradial canals are alike in 

 size and appearance, but in the proximal half the interradial canals are thinner and 

 more slender than the perradial. It is evident that the connection between the 

 interradial and perradial canals is very slight, and probably takes place late in life. 

 The main current from the stomach to the circular canal runs through the perradial 

 canals. From the general appearance of the interradial canals I am inclined to the 

 view that they originate as centripetal canals and that some of them make a union 

 with the perradial canals or the base of the stomach. One specimen shows a slight 

 variation by the presence of two centripetal canals in one quadrant. 



There are about sixteen tentacles ; eight of which are opposite the radial canals, 

 and one is usually present between every two canals. Two specimens have in addition 

 a few very minute tentacular processes, which are evidently tentacles in an arrested 

 state of development. The tentacles (Plate II., fig. 3) are about 10 mm. in length and, 

 although hollow, have rather a stiff appearance. At the distal end there is a large 

 hollow bulb, the ectoderm of which is thickly packed with nematocysts. The basal 

 portion of the tentacles lies in a little groove formed in the margin of the umbrella, 

 and the basal bulb is inconspicuous, just a slight enlargement. One abnormal tentacle 

 with two terminal bulbs was seen ; the extra bulb being on a short lateral branch not 

 far from the distal end. 



There are no indications of any sense organs upon the margin of the umbrella. 



Sibogita borchgrevinki may be distinguished from the other species of the genus by 

 the structure of its gonads, and by the presence of only four (interradial) centripetal 

 canals. 



FAMILY MARGELID^E.* 



Genus KOELLIKERIA, L. Agassiz, 1862. 



RATHKEA (partim), Haeckel, 1879. 



RATHKEA, Maas, 1905. 



Generic Character. Margelidse with four perradial and four interradial groups of 

 tentacles ; and with four branched oral tentacles. 



The genus Rathkea was instituted by Brandt (1838) for Oceania blumenbachi, 

 Rathke, 1835. This is the type species of the genus, and unfortunately it has been 

 inadequately described and badly figured. According to Rathke's figure the Medusa 

 has eight radial canals, eight groups of tentacles, each group having three tentacles. 

 The mouth is shown in a crude drawing which is difficult to interpret. Haeckel, 

 however, defines the genus Rathkea with only four radial canals, and suggests that the 

 other four (interradial) canals in Rathke's figure are probably radial muscle bands. 

 Rathkea blumenbachi was found near Sevastopol, in the Black Sea, and since Rathke 

 described it, no one else has again recorded it. 



* This form of the family name has the sanction of custom only, to which it has been agreed to defer. ED. 



