1 88 CHARLES W. HARGITT. 



Ceratelladse, Gray, thought to belong to the sponges, but later 

 recognized as hydroids. Further comparison convinced the 

 author that his species could not be included under the Ceratel- 

 ladce, hence his institution of the Hydroceratinidae. The follow- 

 ing is his definition of the family: 



"Family HYDROCERATINID/E." 



"Hydrophyton consisting of a mass of entwined hydrorhiza, 

 with a skeleton in the form of anastomosing chitinous tubes: the 

 surface is studded with tubular hydrothecse, into which the 

 hydranths can be completely retracted. Hydranths sessile and 

 connected with more than one hydrorhizal tube, claviform with 

 a single verticil of filiform tentacles. Defensive zooids present 

 with a solid entodermal axis and nematocysts borne at the distal 

 end." 



To one who has any considerable knowledge of hydroid mor- 

 phology it will hardly be necessary to point out the more obvious 

 features in this definition which directly or approximately em- 

 body corresponding features as described in the account of 

 Keratosum. There are, however, certain points in which I am 

 not certain that the definition of Hydroceratinidae would wholly 

 apply to Keratosum. For example, it is stated that "hydranths 

 [are] connected with more than one hydrorhizal tube." I have 

 directed attention to the complex anastomoses of the siphcnal 

 (this term seems more accurate than Spencer's hydrorhizal) 

 tubes but I have not been able to confirm the condition diagram- 

 matically portrayed by his Figs. 3 and 13. It must be noted, 

 however, that my material was not in that vital condition 

 rendering easy and certain the demonstration of a point like the 

 one in question. Still the tubular and hydrothecal relations 

 were such as to render it perfectly sure that the conditions 

 figured by Spencer are lacking in Keratosum. 



But with this difference granted it does not seem sufficiently 

 great to vitiate the many points of agreement which are more 

 fundamental and characteristic as family features. There are 

 also apparent differences as to the nematophores of the two 

 species, yet these are rather specific than even generic and may 

 be disregarded in this connection. Furthermore, there is not in 



