AGASSIZ. NATURAL IIISTORY OF THE UNITED STATES. 483 
Of the five species of true Tubularians just mentioned, three are 
always found in the brackish water of harbours. Two only, Hybocodon 
prolifer and Thamnocnidia tenella choose for their habitat clear open 
rock-pools. 
k. —The genus Corymorpha is of special interest to the zoophy- 
tologist. It is one of the many strange forms described for the first 
time in the classic ‘ Beskrivelser ’ of Sars, and also one of the first 
Hydroids in which the phenomenon of ‘ alternate generation ’ was 
observed. Its typical species, C. nutans , rediscovered by Forbes and 
Goodsir in the British Seas, excels all other simple Hydroids in size, 
and perhaps in beauty. Quite recently its structure and reproduc¬ 
tion have been very carefully investigated by Allman,* and Sars 
himself t has just given us an essay in which no less than seven 
species of Corymorpha are described. 
To these Professor Agassiz has added another, C. pendula , which 
closely approaches the C. glacialis of Sars, resembling this also in the 
fixed character of its medusoids. Male specimens only were observed, 
and the details of the structure of these are by no means complete. 
Curiously enough, Professor Agassiz recognizes but two species of 
Corymorpha , his own and C. nutans ; ignoring, without any comment, 
the other species admitted by Sars. 
l. —Cavolini, in his famous work, gave a figure and description 
of a supposed Sestularian, S. pennaria , for which Goldfuss after¬ 
wards constituted a separate germs. The name Pennaria is certainly 
appropriate, this zoophyte exhibiting a shaft-like tapering stem, from 
the scarcely perceptible zig-zag bends of which arise, on either side, 
rows of alternating branches, bearing the polypites. Pennaria , 
however, is chiefly interesting because of its zoological position, since 
it seems to connect together the two principal sections of the 
Corynoid group, J represented by the genera Tubularia and Coryne , 
respectively. As in the former each polypite possesses a single 
circlet of long proximal tentacles, but these are not, like those of 
Tubularia , set round the margin of a well-marked disk. On the 
other hand the distal region of the polypite is largely developed, 
forming a conspicuous probocis, the oral end of which is u covered 
by numerous short, globe-tipped tentacles.” The medusoids, which 
are few' in number, arise independently of one another, each upon a 
short stalk, immediately within the proximal tentacular circlet. 
“ What seemed to distinguish this medusa [in P. gibbosa~\ from all 
other Medusae, among the Tubularians, was the position of the ovaries, 
which, instead of being on the proboscis, were near the peripheric, 
or outer end, of the chymiferous tubes ; these organs were, however, 
not so far developed as to show their sexual character, and may be 
* Notes on the Eydroida , A. N. H. January, 1863. 
t ‘ Ueber das Ammengeschlecht Corymorpha und seine Arten, nebst den von 
diesen aufgeammten Medusen’, Wiegm. Arch. 1860, p. 347 [translated in A. N. H. 
Nov. 1861]. 
X Coryniche of Huxley, Tubularina of Ehrenberg and Johnston. 
