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PROCEEDINGS OF THE 



[April, 1857. 



than the Oceanidae proper, and the Sarsiadae. The Trachynemidae 

 and Geryonidae of Gegenbaur and the JEquoridas, can never be 

 well located until we become better acquainted with their embry- 

 ology, But it appears to me the Aequoridae are certainly very 

 closely related to the last family of Gegenbaur, the Aeginidae, 

 which no doubt constitute a family apart. 



It is evident also from the name which Gegenbaur applies to this 

 order, Craspedota (provided with a veil,) that he does not take 

 into consideration those lower forms of Hydroidea which never 

 attain so high a degree of complexity. All the Sertularians, 

 proper, Clava and Hydractinia are left out by this mode of draw- 

 ing the bounding line, and consequently do not appear among his 

 families. The Siphonophorse also with the exception of Chryso- 

 mitra find no place among these families. 



In attempting to group the Hydroid Medusas of Charleston 

 harbor into families, I have of course been led to consider many 

 forms which are not found in our waters, and it appears to me that 

 families in this group are founded on certain apparently slight 

 modifications in structure and combination of organs both in the 

 larva and adult — that members of the same family of Medusae are 

 derived from hydroid larvae of one type, or not differing from 

 each other more than generically and that frequently on account 

 of the low grade of development of the adult form, it is more easy 

 to determine the family from the characters of the larva than from 

 those of the adult. Thus Tubularia coronata, according to Van 

 Beneden, produces medusa buds, which never become free; the 

 same is true of a species in Charleston harbor, while the two other 

 species described by Van Beneden, both produce free medusae. 

 The Medusae which never become free, have no tentacula, while 

 those that swim freely have them ; yet certainly in spite of their 

 differences of structure and condition, they belong to one family. 

 Again, Sarsia and Callichora (Oceania ?), differing as they do in 

 structural details, are all developed from Corynidae, and it is al- 

 most impossible to decide whether such groups should hold the 

 position of families or of sub-families, while from this group of 

 Corynidae I doubt whether it would be proper to exclude even 

 Clava. In the same way Tiaropsis, an ocellated genus, belongs 

 to the same group as Eucope, which is unocellated, for both are 

 developed from Campanulariae. The genera Nemopsis, Bougain- 

 villia and Lizzia, on the other hand, seem to constitute a natural 

 family, having fasciculated marginal tentacula and branching 



