VoL. 2] Torrey.—Hydroids of the San Diego Region. 23 
margin of the hydrothecae and the intrathecal origin of the 
gonangia. 
Are these characters of equal rank? Evidently Nutting pre- 
fers the latter, since he does not hesitate to align such a smooth 
round margined species as S. formosa with the typical dentate 
operculate species of Sertularella. Here I can by no means agree 
with his judgment, but must take the ground which I previously 
oceupied (:02, p. 62). The mere location of gonangia, whether 
arising within or outside of hydrothecae, cannot to my mind be 
of such taxonomic importance as the striking differences of the 
trophosomes in species like S. halecina and S. tubitheca; though 
I am far from refusing its aid as a means of distinguishing 
species. 
The general grounds which I formerly urged against Syn- 
thecium need not be repeated here. I am still in hearty accord 
with the position then taken, but a review of actual conditions 
in S. halecina may prove more convincing. In the majority of 
cases, the gonophores of this species arise within hydrothecae. 
Oceasionally, however, they are borne directly on the stolon 
(fig. 14), as in Dynamena cornicina. When such a difference in 
the position of the gonangia exists in different species, it has 
been held by Allman and Nutting to indicate generic distinction. 
For instance, Sertularella integritheca, with smooth round mar- 
gined hydrothecae and extrathecal gonangia, is said to be gene- 
rically distinct from such a form as Synthecium alternans All- 
man, with intrathecal gonangia but otherwise similar to S. integ- 
ritheca. Occasional conditions such as the intrathecal origin of 
gonangia in species in which the gonangia are usually extra- 
theeal, are held by the same authors to be abnormalities which 
may be disregarded in classification. The extrathecal origin of 
the gonangia of S. halecina’ being but occasional, would natu- 
rally find a place in the same category. These views do not 
appear to me to be justifiable, for the occasional presence of 
extratheeal gonangia must lessen the importance of the usual 
condition, and should not be disregarded for this very reason. 
‘Tf it be objected that the extrathecal gonangia in S. halecina arise on 
the stolon instead of the stem, it may be remembered that stem and stolon 
are fundamentally the same structure, and transform into each other with 
the utmost readiness. 
