28 bulletin: museum of comparative zoology. 



As was shown by Maas, 1893, these Trachyhna forms range widely over 

 the open ocean ; and this observation has been confirmed by us during 

 the cruise of the U. S. F. C. S. " Albatross " in the Tropical Pacific, 

 1899-1900. 



The Siphonopliorae of the Tortugas are very closely related to those of 

 the Canary Islands. They also display a relationship to those of the 

 Fiji Islands, South Pacific. 



The Scyphomeduste of the Tortugas are, for the most part, distinctly 

 West Indian types, and are not closely related to forms known from the 

 African coast. 



33 Hydromedusse, 3 Siphonophorse, 1 Hydroid, and 2 Scyphomedusae 

 are new to science, and 44 forms are new to American waters. 



DESCRIPTIONS OF SPECIES. 



I. HYDEOMEDUSiE. 



DIPURBNA, McCrady, 1857. 



Dipurena fragilis, nov. sp. 



Fig. 41, Plate 17. 



Specific Cliaracters. — The bell is 4 mm. in height, and is half egg-shaped. 

 The bell walls are of only moderate thickness. There are 4 long slender 

 tentacles each bearing upon its distal end a single knob-shaped mass of nema- 

 tocyst cells. A single black ocellus is situated in the ectoderm of the outer 

 surface of each tentacle bulb. The velum is prominent. There are 4 slender 

 straight radial canals, and a narrow ring-canal. The proboscis is about 8 mm. 

 in length, and exhibits two distinct annular swollen regions where the gonads 

 are situated. The entoderm of the proboscis, and of the basal bulbs of the 

 tentacles, is ochre-yellow. The entoderm of the distal nematocyst knobs of 

 the tentacles is slightly orange. Several specimens were found at the Tortu- 

 gas in June, 1897. 



This species differs from Dipurena strangulata of Charleston (see McCrady, 

 Proc. Elliott Soc, 1857, p. 33, Plate 9, Figures 1, 2) in that the tentacles are 

 longer and much more slender ; and the color of the entoderm of the proboscis 

 and tentacles is light ochre-yellow instead of rich green and red as in the 

 Charleston species. 



