MAYER: MEDUSA FROM THE TORTUGAS, FLORIDA. 79 



swimming-bell is long and tube-like, and its axis is parallel to that of the bell 

 cavity. Indeed, it is quite similar in form to the hydroecium of Abyla 

 quincunx (see Figure 115, Plate 34). The first appendage of the siphosome is 

 the posterior swimming-bell. This is somewhat larger than the anterior and 

 is five-sided, the sides being bounded by prominent, angular, serrated ridges. 

 There is a single median dorsal ridge and two pairs of lateral ridges. The 

 ventral-most pair of lateral ridges are wing-like, and enclose a trough-like 

 groove through which the siphosome extends. The bell ca\n^ty of the posterior 

 swimming-bell is spindle-shaped and is provided with 4 radial tubes and a 

 circular vessel. These are placed in communication with the general gastro- 

 vascular cavity of the siphosome by means of a long slender duct. The 

 posterior swimming-bell is furnished ^vith a powerful velum, by the con- 

 tractions of which the animal is enabled to shoot through the water. The 

 siphosome is not very long and rarely extends beyond the posterior extremity 

 of the trough-like groove in which it lies. The first organs to be developed 

 upon it are the feeding-polypites ; the tentacles soon arise as buds from the 

 sides of the polypites, each feeding-polypite being provided with a single 

 tentacle. The tentacles give rise to lateral branches each one of which termi- 

 nates in a swollen cylinder-shaped nematocyst battery. 



A long, slightly curved, bristle-like spine arises from the siphosome at a 

 short distance below its origin, and extends outward to a considerable distance 

 beyond the distal end of the posterior swimming-bell. It seems probable that 

 this structure may be morphologically equivalent to a bract, that has become 

 thus modified for defensive purposes. Other covering scales or bracts were 

 observed upon the siphosome, but these were leaf-shaped (see c .s. Figure 90, 

 Plate 27). No gouophores or sexual organs were observed, and the sexual 

 generation is unknown. 



This rare form is found among the Bahama Islands during the winter 

 months. The specimen from which we have obtained our figure was captured 

 in Nassau Harbor, New Providence Island. We also obtained a specimen at 

 Watlings Island (San Salvador) on January 15, 1893. 



AGALMA, EscHscHOLTz, 1825. 



Agalma Pourtalesii, Agassiz and Mater. 



Figures 106-113, Plates 31-33. 



Agalma Pourtalesii, Agassiz, A., and Mayer, A. G., 1899; Acalephs from the Fiji 

 Islands, Bull. Mus. Comp. Zool. at Harvard Coll., Vol. XXXII. p. 180. 



Specific Characters. — The entire animal (Plate 32) is about 25 mm. in 

 length. The feeding-polypites, dactylozoids, tentacles, and gonostyles, all arise 

 from the ventral side of the siphosome. The float, or pneumatophore, is of 

 small size, and its apical pore is surrounded by radially arranged streaks of dark 



