260 BULLETIN : MUSEUM OF COMPAKATIVE ZOOLOGY. 



dusa after sexual maturity is reached ; and it is liy no means improbable that 

 the same may be true here. As in the case of the velar canals of Charybdea, 

 so here the number and even form of the blind centripetal canals are probably 

 chiefly dependent upon age, and cannot be considered of much systematic 

 importance. 



Pegantha simplex, sp. nov. 



Plate 5, Figs. 19, 30. 



This Medusa has the form characteristic of the genus. The bell consists 

 of a thick, lenticular central portion, surrounded by a dependent ring or collar, 

 from which it is divided by a shallow furrow. The margin of the collar is 

 divided into eight lappets, each of which is in turn subdivided into two by 

 a shallow groove. The lappets are very flexible, and can be curved inward, 

 so that they nearly close the bell opening. The bell is about three mm. 

 in diameter, and one half as high as broad. There are only eight tentacles, 

 a much smaller number than has been reported for any other species of the 

 genus ; and this number seems to be constant. They arise from the periphery 

 of the central disc, alternating with the eight marginal lappets, and correspond- 

 ing to the grooves between them. They are broadly conical at the base, solid, 

 carried curved stiSly outward, and are slightly longer than the bell is high. 

 They taper very rapidly, and toward the tips are very delicate. A charac- 

 teristic feature of this Medusa, in which there are no radial canals, is the 

 large size of the stomach. This organ, which is lenticular in cross-section and 

 provided with a broad, simple mouth without lips, extends to the periphery 

 of the central disc. In outline it is somewhat octagonal, the angles being 

 opposite the tentacles, and from the middle of each side (alternating with the 

 tentacles) it throws out a narrow canal running to the corresponding gonad, 

 one of which lies at about the middle of each marginal lappet. The gonads 

 are sac-shaped bodies, of considerable size, suspended from the surface of the 

 subumbrella. In this Medusa they are simple, although in most other species 

 of the genus they are subdivided into three or more secondary lobes. There 

 are about two hundred otocysts, situated on the edges of the marginal lappets, 

 about twenty-five to each lappet. Each otocyst arises from a low and broad 

 "auditory papilla," which is thickly set with short stiff ciliae. The otocysts 

 themselves are oval, and contain three rather long prismatic otoliths. At 

 their bases they bear club-shaped processes, about twice as long as the otocyst, 

 which extend up into the substance of the bell. When the lappets are retracted 

 over the bell opening, these processes alone are visible. 



The Medusa is altogether colorless. An a1)undant species : numerous 

 specimens, Decend)er 26, Male atoll, near Male island ; January 2, off 

 the east face of Kolumadulu atoll, in an open net at fifty and one hundred 

 fathoms ; January 15, Malosmadulu atoll, surface. One of the few species 

 which appeared to be equally common inside and outside the atolls. 



