Chap. VII. OBELIA COMMISSURALIS. 315 



in Pis. XXXIII. and XXX. complete each other; some figures of L. amphora 

 reproducing stages intermediate to those figured for Obelia. As the description 

 of the plate will sufficiently elucidate their character, we may simply enumerate 

 them in the order of their relative state of development. Thus, the youngest 

 is PI. XXXIII. Fi(j. S'' ; then PI. XXX. Fig. 8, the base of a branch ; PI. XXXIII. 

 Fig. 3, a branch and the base of a pedicel ; PI. XXX. Fig. 9, a calycle half 

 grown; PI. XXXIII. Fig. 4, a calycle three quarters developed; PI. XXX. Fig. 10, 

 just before the tentacles begin to form; PI. XXX. Fig. 11, somewhat contracted, 

 and Fig. 12, the calyx fully shaped out, and the rim, from which the tentacles 

 arise, quite sharp, and Fig. 13, the same as the two last figures, showing the calyx 

 broadened at the base by the strongly-retracted hydra; PI. XXXIII. Fig. 7, the 

 tentacles just beginning to develop. Fig. 0, tentacles further advanced, and, finally, 

 Fig. 8, the tentacles complete, and the operculum of the calyx upon the point of 

 falling off. 



SECTION VI 



OBELIA COMMISSURALIS McCR. 



Proles hgdroidea. AdiiU. — The hydrarium of this species is a littoral animal, 

 and may be found at low tide along the rocky shores of the Atlantic Ocean, 

 from Nova Scotia to Charleston, South Carolina, attached to stones, or sea-weeds 

 of various sorts. It rises from its base to a height of at least five or six inches 

 (PI. XXXIII. Fig. 1), but is certainly in an adult state even when not more than 

 an inch high {Fig. 2), inasmuch as, at that age, it bears medusoe, in the proper 

 season. In its mode of branching it comes nearer to Laomedea dichotoma of the 

 European shores, as figured by Johnston in his " British Zoophytes," 2d ed., PI. 

 XXVI. Figs. 1 and 2, p. 102, than to any other species thus far described. Van- 

 Beneden's figure of the European species, under the name of L. geniculata, Mem. 

 Acad. Brussels, 1844, Vol. XVII., is better than that of Johnston's. The most 

 closely-alHed species, towever, is tliat described by Cavolini, " Memorie, &c., &c., 

 polipi marini, Naples, 1785, Tab. '8, Figs. 1, 2, 3, and 4," under the name of Sertu- 

 laria geniculata ; ^ for, in this species, not only are the reproductive calycles identical 



1 McCrady has already described out species and I have no doubt that the Obelia sphajrulina 



without, however, giving a full account of its devel- figured by Slabber, and quoted by Peron and 



opment. He was, nevertheless, right in restoring LeSueur, is the free medusa of the Hydroid de- 



the name of Obelia Per. and LeS. to this type, scribed by Johnston and VanBeneden. 



