1894.] Hydyoid: Cold Spring Harbor, Long Island. 33 
of the branching, together with the origin of the meduse from 
the stalks bearing the hydroid members, and the presence of 
several meduse originating at a common point of attachment 
to the parent stem are the specific characters that have required 
the erection of this new species. 
For convenience the species of the genus are summarized 
here. 
P. repens, tentacles all erect, about 18-20, meduse and 
hydroids simple, arising separately from a creeping hydro- 
rhiza, young medusa bi-tentaculate. 
P. minutus, tentacles 7, meduse arising from the simple or 
very sparingly branched hydroid persons, on shells of Turri- 
tella. i 
P. vestitus, tentacles 8, alternately reflexed, medusæ arising 
either from the hydrorhiza or from the hydroid person, not in 
clusters; hydroids not branched, young medusa bi-tentaculate, 
On shells of Buccinum. 
P. palliatus, tentacles, 8 alternately reflexed, thick gelatinous 
coat as far as the bases of the tentacles, gonophores arising from 
the hydrorhiza. On shells of the hermit crab. 
P. jonesii, tentacles 16, alternately reflexed, thick gelatinous 
coat as far as the bases of the tentacles; meduse and hydroids 
on the same stalks, hydroids luxuriantly branched and 
mudusz clustered, young meduse bi-tentaculate. On shells of 
Libinia. ; 
To the morphologist a form like the one just described has 
peculiar interest because of the many primitive characters 
which are united in it. It is not improbable that the higher 
calyculate Campanularian Hydroids may have been descended 
from athecate ancestors that were more or less closely like the 
genus Perigonimus. This is a very lowly form of the tubular- 
ians, having only a single row of tentacles, the mode of repro- 
duction is very simple, and the medusa is of a most simple char- 
acter. Still while Perigonomus is treated among the naked 
hydroids, it has a covering. This covering is such a one as 
such an animal as the naked hydroids might have in their 
earlier stages of the acquisition of a strong skeleton. It is not 
a highly differentiated product, but a delicate, hardly com- 
pacted slime not very unlike the mucous secretions that all . 
3 
