146 THE MEDUSAE. 



Halitrephes maasi, sp. nov. 

 Plate 33, figs. 1-5, 7, 10; Plate 45, fig. 13. 



Station 4646; 300 fathoms to surface; fragmentary, only the disc. 



Station 4653; 300 fathoms to surface; fragmentary, only the disc. 



Station 4668 ; bottom of Tanner net; from about 300 fathoms; type 

 specimen, in fairly good condition. 



Unfortunately the type specimen alone is in good condition, the other 

 two being so fragmentary that their identification is doubtful. 



Diameter of the type 55 mm. The exumbrella surface is smooth and 

 rounded ; the bell low ; the gelatinous substance thin and very brittle ; the 

 subumbrella cavity shallow. 



Tentacles. — These are of different sizes, though structurally all alike 

 (PI. 45, fig. 13). They show the characteristic separation into proximal 

 and distal portions in less marked degree than other members of the 

 family. This may, however, be due to the rather soft condition of the 

 specimen. The distal portion of the tentacles, though thinner and stiffer 

 than the proximal (PI. 33, fig. 2), is less spine-like than in Halicreas. The 

 differentiation of the entodermal core into two regions is sharp. The ecto- 

 dermic layer of the distal portion, which is rather thick and densely crowded 

 with nematocysts (PI. 33, fig. 7), is preserved in many of the tentacles. 

 AVhen it is partially destroyed the stiff core is i-evealed. All the ten- 

 tacles, even the smallest, arise from triangular entodermic roots ; those of 

 the larger ones extending across the circular canal. There are about 

 seventy tentacles of various sizes ; usually one lies opposite each canal. 

 Many of them are broken short off, as is seen in the general view (PI. 33, 

 fig. Ji). 



Otocysts. — These, as in other members of the family, are free clubs, 

 consisting of an ectodermic sheath and entodermic core. I have not been 

 able to determine on the specimen (preserved in formalin) whether oto- 

 liths were present, but the appearance of the sense organs suggests that 

 they contained one or two such structures (PI. 33, fig. 10). They are easily 

 distinguished from small or rudimentary tentacles by their definite form, 

 imiform size, and by the fact that they lack the entodermic roots character- 

 istic of the latter. On account of the condition of the margin I was unable 

 to count the otocysts ; but they are certainly much less numerous than the 

 tentacles (PI. 45, fig. 13). 



