MUSEUM OF COMPARATIVE ZOOLOGY. 215 



reasons which led me to regard the published figures of the adult as the 

 young, and not the adult Nanomia.* One of the most important reasons 

 which have influenced me is the small size and the small number of nectoca- 

 lyces. While the specimen figured is barely six inches long, specimens of 

 Nanomia were often found at Grand Manan four and five feet in length. 

 While A. Agassiz never found more than four pairs of fully developed nec- 

 tocalyces, many of the adults had fifteen pairs of these structures. 



A more important fact, however, which would seem to indicate that the 

 figure is that of a young animal, is the following. The great number of em- 

 bryonic tentacular knobs,t or those described on the " first set of polyps," 

 show immaturity ; for these knobs are always confined to young or larval 

 forms in related genera, like Agalma, Halistemma, and Stephanomia. The 

 adult permanent knobs, or "corkscrew-shaped tentacles," are aU immature. 

 The adult form of these knobs is not attained in any of those of Nanomia yet 

 figured. 



In order to facilitate the reader in a comparison of my description with that 

 in the " North American Acalephae," the following table is introduced. The 

 terms in the first column are from the published account, those in the second 

 are made use of in the present description . 



First set of polyps Embryonic polypite with embryonic ten- 

 tacular knobs. 



Second kind of polyps ..... Undeveloped permanent polypites with 



undeveloped permanent knobs. 



Third kind of polyps Hydrocyst, taster. 



Fourth kind of appendage (p. 206) Undeveloped hydrocyst, taster. 



The largest specimen captured measured, when extended, over four feet; 

 when retracted, its length was three feet. The specimen which is figured, ot 

 life size (Plate I.), was one of the most convenient for study, but not one of 

 the largest. It may safely be said that hundreds of specimens of the size 

 represented were taken just off the wharf near the Dominion House at 

 North Head, Grand Manan. 



The adult animals, as they float extended in the water, can readily be dis- 

 tinguished by a practised eye from the southern Physophore, Agalma elegans. 

 The whole external appearance of the two genera is different. The tentacles 

 of Nanomia are carried in a different way from those of Agalma, and are not 

 drawn to the polypites in the same clumps, while the tentacle itself is more 

 often thrown into festoon-like folds, as shown in the figure. It is needless 



* North American Acalephae, Illust. Cat. Mus. Comp. Zool., No. 2, p. 201, 

 Fig. 332. 



t On many of the small specimens of Nanomia from Grand Manan, embryonic 

 knobs (Plate II. Fig. 8) were found. These closely resemble the knobs figured by 

 A. Agassiz. They were not found in adults as far as observed. 



