388 THE AMERICAN NATURALIST. | [Vor. XXXIV. 
name under which it is now known. |. L. Agassiz early pointed 
out nomenclatural objections to the name Globiceps of Ayers, 
and Eucoryne of Leidy, and at the same time indicated certain 
. differences between the diagnostic characters of this hydroid 
and those originally designated as distinctive of the genus by 
Cavolini and Goldfuss. A. Agassiz (65) in the catalogue of 
the North American Acalephz has, however, followed the des- 
ignation of McCrady, and has in turn been followed by most 
American students of the Hydroidea. 
Still later, however, Allman (71) took up the suggestion of 
the elder Agassiz concerning the unavailability of the generic 
terms Globiceps and Eucoryne and, discrediting the conten- 
tion of McCrady as to the identity of the form with that of 
Pennaria, proposed the new generic name Halocordyle. He 
bases his claim for such distinction wholly upon the apparent 
difference as to the arrangement of the arms, or tentacles, 
those of the hydroid under consideration being distributed in 
verticillate whorls about the hydranth, while those of Penna- 
ria gibbosa have them somewhat promiscuously distributed 
over the body of the polyp. 
It might be sufficient warrant for doubt as to Allman's con- 
tention that his diagnosis is based chiefly upon published fig- 
ures of the hydroid, having in neither case had access to living 
specimens. And when added to this there is recognized the 
further fact that a careful study of several species from differ- 
ent regions, and from the same region, shows all degrees of 
intergradation in these respects, an unhesitating dissent from 
Allman's view will not be regarded as extravagant. 
IL MATERIAL AND METHODS. | 
The material chiefly used was obtained at Woods Holl dur- 
ing the summers of 1897, 1898, and 1899, and in almost un- 
limited quantities. Material of P. Cavolini was secured and 
preserved by the writer from the Bay of Naples in 1894, and 
was used in many points of comparison, as will be indicated in 
appropriate phases of the paper. In general, collections were 
made at low tide and in the waters in and about the harbor, 
