HYDRAID^. 197 



Family HYDRAID^ Gray. 



Hydraidce Gray. Syn. Brit. Mus., p. 7G. 1840. 

 Hi/drina Ehrenb. (jo. p.). Corall. d. Roth. Meeres, p. 67. 

 Hydraidce Joilnst. Brit. Zooph., p. 120, Second Edition. 



HYDRA Linn. 



Hydra Linn. Syst. Nat. 1756. 



Hydra gracilis Agass. 



Hydra gracilis Agass. ; in Proc. Best. Soc. Nat. Hist., III. p. 354. 

 Hydra gracilis Ayres ; in Proc. Bost. Soc. Nat. Hist., V. p. 103. 



Our fresh-water Hydra has as yet been studied so insufficiently, 

 that I am unable to add anything respecting the development of the 

 Medusae, or concerning its identity with the European Hydra viridis. 

 Agassiz has described two Eastern species under the name of Hydra 

 gracilis and H carnea, and Ayres a California species. From the 

 character of the Medusae of the Hydra, it seems to me that it finds 

 its natural place among the true Hydroids, and not among the Dis- 

 cophor£e, with which it has usually been associated, on account of its 

 close resemblance to the Scyphistoma (Hydra tuba). 



Cambridge (L. Agassiz). 



Cat. No. 370, Cambridge, 1862, W. Glen. 



Hydra carnea Agass. 



Hydra carnea Agass. ; in Proc. Bost. Soc. Nat. Hist., HI. p. 354. 

 Hydra carnea Ayres ; in Proc. Bost. Soc. Nat. Hist., V. p. 104. 



Massachusetts and Connecticut (Agassiz ; Ayres). 



Hydra tenuis Ayres. 



Hydra tenuis Ayres ; in Proc. Bost. Soc. Nat. Hist., V. p. 104. 



San Francisco, California (Ayres). 



