NO. 2114. EPERETMUS, NEW GENU^S TRACHOMEDUSAE—BIGELOW. 403 



ones successively lower and lower down. The tentacles are soft and 

 flexible, the outer part of the older ones ringed with nematocyst 

 ridges (fig. 6, 7). Few, if any, of the latter form complete rings; but 

 no defuiite zone is free from them, a character in which the tentacles 

 agree with the primary, but not the secondary, tentacles of Olindias, 

 and with the tentacles of Gonionemus. The basal half of the large 

 tentacles is smooth. In the young tentacles the smooth portion is 

 relatively shorter; in the youngest the whole length is ringed with 

 nematocyst ridges. The tips of aU the tentacles, young and old, 

 bear spherical knobs composed of closely crowned nematocysts, 

 radially aj"ranged; a termmation very different from the suckers on 

 the primary tentacles of Olindias, but suggesting the terminal knobs 

 of the secondary tentacles of that genus; and practically mdistinguish- 

 able from the tips of the tentacles in Nauarchus and Gossea. 



The otocysts alternate roughly with the tentacles (fig. 2) instead 

 of lying close to them, as in Olindias, and are about as numerous, i. e., 

 a total of about 160; like the tentacles, they show various stages m 

 development from newly formed to adult. Structurally the sense 

 organs closely resemble those of Olindias and Olindioides (Goto 1903) ; 

 each consisting of an otolith, apparently enclosed by a thin proto- 

 plasmic layer, situated on a short protoplasmic stalk containing 

 nuclei, but without visible cell walls. The organ is enclosed in a 

 thin walled capsule, situated in close contact with the outer edge of 

 the aboral wall of the circular canal, the whole deeply imbedded in, 

 and entirely enclosed by the gelatinous substance of the bell. The 

 position of the otooyst and its relation to the tentacle root, nerve 

 ring, and ciicular canal is shown by a radial section through the disk 

 (fig. 8). The otocysts differ from those of Olindias, in uivariably 

 having one otolith only, as seems to be the case in Olindioides also. 



Color. — In the preserved state the nematocyst pads at the base of 

 the largo tentacles, the manubrium, and gonads are pale, but opaque 

 yellow; otherwise the specimen is colorless. 



BIBLIOGRAPHY. 



li)09. BiGELOW, H. B. Reports on the Scientific Results of the Expedition to the 

 Eastern Tropical Pacific, etc., XVI. The Medusae. Mem. Mug. Comp. 

 Zool. Harvard Coll., vol. 37, pp. 243, 48 pis. 



1912. . Preliminary account of one new genus and three new species of 



Medusae from the Philippines. Proc. U. S. Nat. Mus., vol. 43, pp. 253-260. 



1913. . Medusae and Siphonophorae collected by the U. S. Fisheries 



Steamer "Albatross" in the Northwestern Pacific, 1906. Proc. U. S. Nat. 

 Mus., vol. 44, pp. 1-119, pis. 1-6. 



1904. Browne, E. T. Hydromedusae, with a ReArision of the Williadae and Petaai- 

 dae. Fauna and Geography of the Maldive and Laccadive Archipelagoes, 

 vol. 2, pp. 722-749, pis. 54-57. 



190o. = . The Medusae. Suppl. Rep. 27, Pearl Oyster Fisheries of the 



Gulf of Mannar. Roy. 8oc. London, pp. 131-166, 4 pis. 



