AGASSIZ. NATURAL HISTORY OF THE UNITED STATES. 487 
Of the third family of Campanularians no species is here de¬ 
scribed. Its type is the Campanularia dumosa of Fleming. This 
species, “which belongs to the genus Lafoea of Lamouroux, pro¬ 
duces Medusae without eyes at all, one of which has been described 
as Atractylis repens by Mr. Wright.” “ My son (continues Pro¬ 
fessor Agassiz) has lately traced the development of a species of 
Hydroid from our coast, which I have identified with Lafoea cor- 
nuta, Lamrx., the type of the genus, originally found in Newfound¬ 
land. This establishes, beyond a doubt, the fact that there are 
several families among the Hydroids thus far referred to the genus 
Campanularia/ ’ 
Dynamena [ Sertularid ] pirnila , the last fixed Hydroid of which 
Professor Agassiz treats, is also remarkable as being the only one of 
whose specific identity with its European representative (living spe¬ 
cimens of which were procured and carefully examined), he is now 
thoroughly assured. It is, morever, the most common American 
form of its genus, and the sole example of the second primary 
division of the Sertularina, including all those genera with sessile 
polypites, here described. 
To the Siphonophora Professor Agassiz devotes but four pages, 
in which, after some general remarks on the sub-divisions of 
the group, a brief account is given of the North American 
Physalia , P. Arethusa. This species, when floating, always turns 
to the windward side that aspect of its body along which are 
arranged the largest tentacles ; “ and when the breeze is fresh, 
and the animal is driven before the wind, these tentacles are 
stretched to a most extraordinary length, varying, according to cir¬ 
cumstances, from twenty to thirty, forty, and even fifty feet, and 
forming as many anchors upon which it rides, without being cast 
adrift.” “ I have observed them [he adds,] in stormy weather strug¬ 
gling in that way against the elements, in order to avoid being 
thrown ashore. It is curious to see how, under these circumstances, 
they change their position, by raising the pointed end of their air¬ 
bag, and throwing themselves suddenly upon the opposite side; but 
I have never seen them emptying their bag and sinking under the 
surface of the water.” The general form of this Physalia is repre¬ 
sented in a very beautiful plate. Few structural details are given. 
Want of space at the end of the present volume forbids Pro¬ 
fessor Agassiz from enlarging further on the North American Sipho¬ 
nophora, which “ for many years past,” he has had “ ample oppor¬ 
tunities of investigating.” We gladly, therefore, accept his promise 
to resume his “ communications, upon this subject, on another occa¬ 
sion.” 
In the “ Tabular View,” with which Part IV. terminates, the 
genera, families and sub-orders of the Hydroidce are thus given:— 
