482 
REVIEWS. 
tom, so as to become a short, almost globular mass, with several 
transverse folds overlying each other, and extending from the base 
at least half way up the stem. When the tentacles are contracted, 
also, the whole body resembles a warty excrescence.” The repro¬ 
ductive bodies are unknown. 
f—j. — Hybocodon , Parypha and Thamnocnidia are merely subdivi¬ 
sions of Tubularia , from which Professor Agassiz has here, for the 
first time, separated them. “ The genera differ from one another, 
chiefly by the form and arrangement of the tentacles of the proboscis, 
and the structure of the medusae-buds.” The distinctions on which 
Professor Agassiz here insists do not, when compared with his 
figures, appear to us to be of generic rank. Of the British species, 
T. indivisa remains in Tubularia proper; T. coronata and T. calamaris 
are referred to Thamnocnidia , while a new genus, iEctopleura, is con¬ 
stituted for T. JDumortieri. 
Hybocodon prolifer produces free reproductive zooids, closely 
resembling the Euphysa and Steenstrupia of Forbes, and the medusoids 
described by Steenstrup as budded from his Coryne fritillaria. The 
proboscis of the hydroid form is furnished, in adult specimens, with 
thirty-two tentacles, arranged in two rows, those of the upper or 
distal circlet, closely surrounding the mouth, being only half as long 
as those of the second circlet, situate a short distance below it; “ and 
the decurrent bases of the latter alone form the broad, parallel ridges, 
which lie closely, side by side, about the circumference of the pro¬ 
boscis.” The tentacles of the two rows alternate, but are occasionally 
thrown together so as almost to constitute a single series. 
Parypha crocea has twenty-four buccal tentacles placed in a single 
row. “ They are cylindrical, and tapering from the base to the tip, 
which is rounded off in an oblique manner. At their bases they 
touch each other, and thence are decurrent, in juxtaposed broad 
ridges, which give the proboscis a longitudinally ribbed appearance. 
The upper side of the bases of these tentacles project in approximated 
ridges to the very edge of the mouth, just in the same manner as 
obtains in Thamnocnidia spentabilis and T. tenellaP Between the 
hydroids of these three species there scarcely exists any difference, 
and in all the medusoids remain attached. Those of Parypha crocea 
present an extremely simple structure, without any traces of a canal 
system, and the females only possess tentacles. In the medusoids of 
Thamnocnidia , “ around the lower edge of the disk, are three or four 
solid, short, and rather unshapely tentacles.” T. tenella , the smallest 
of the AmericanTubularians, differs from T. spectabilis merely in size, 
habit, and mode of branching. 
Tubularia Couthouyi is a close ally of the well known T. indivisa. 
As in that species, the reproductive bodies are fixed. The buccal 
tentacles of the hydroid are about fifty in number, and “ are disposed 
in three or four indistinctly defined series. In each series they are 
successively shorter than the next inner, or higher ones, and the 
outermost are mere papillae,” 
