54 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



This medusa is very common throughout the summer months at the Tortu- 

 gas, Florida. On July 22, 1898, a great swarm of them appeared, and were so 

 abundant that one could not dip up a bucketful of sea- water without captur- 

 ing several specimens ; and two such swarms came in the summer of 1899. 



This is the only Hydromedusa known which is normally formed upon the 

 plan of live (pentamerous). It seems very probable that it has arisen, phylo- 

 genetically, as a sj)ort from some species of Epenthesis or Oceania, some indi- 

 viduals of which made their appearance -with 5 radial canals instead of 4 ; and 

 these abnormal individuals succeeded in perpetuating a new species. Bateson 

 (1894; Materials for the Study of Variation, p. 425) calls attention to an ab- 

 normal specimen of Sarsia mirabilis having five complete segments, and says 

 that " there is perhaps in the whole range of natural history no more striking 

 case of the Discontinuity and perfection of Meristic Variation. In the case of 

 Eucope (Obelia) it has been shown by Agassiz and Woodworth (1896 ; Bull. 

 Mus. Comp. Zool. at Harvard Coll., Vol. XXX. p. 121-150, 9 Plates) that 

 among 3,917 niedusge 9 had three radial canals, 20 had five, and 3 had six 

 radial canals. It thus appears that in Obelia the tendency to produce sports 

 having 5 radial canals is about twice as great as that to produce individuals 

 with any other number of canals. Yet sports of Obelia with 5 radial canals 

 have not succeeded in perpetuating a new species. 



I have made careful observations of 1000 individuals of Pseudoclytia pen- 

 tata, and find that 70.3% are normal (i. e. have 5 canals 72° apart, 5 gonads, 

 and 5 lips to the proboscis). The remaining 29.7% are abnormal in some 

 respects, and a large number of the abnormalities tend toward the ancestral 

 condition of 4 canals and 4 lips. The medusa is very much more variable 

 than the 4-rayed Epenthesis foUeata at the Tortugas, and its greater variability 

 may be due to the fact that being a new form it displays a greater tendency 

 toward variability in various directions. This question will, however, be 

 made the subject of a special paper. 



MULTIORALIS, nov. gen. 

 Multioraiis ovalis, nov. sp. 



Figs. 139, 130, Plate 39. 



Generic C7mrac<ers. — Multioraiis. Leptomedusge having a circular canal, 

 and a single, simple chymiferous canal which extends across the sub-umbrella. 

 A number of separate manubria are situated upon the chymiferous canal. 



Sjoecijic Clmracters. — Adult medusa. The bell is quite flat, and is ellipti- 

 cal in outline, the major axis being 4 mm. and the minor 2.4 mm. The gelati- 

 nous substance is not very thick and is ([uite flexible. There are 20-25 short, 

 simple, coiled tentacles with well-developed basal l)ulbs. These tentacles are 

 only about one half as long as the minor axis of the bell. There are no lateral 

 or mar^'inal cirri. The otocysts are slightly more numerous than the tenta- 



