of the SerUilaria Gelatimsa of Pallas. 3T 
iy the Cellipora pumlcosa in its perfect state. This new spe^ 
cies, which I have termed F. unicornis, spreads its thin crust 
on fuci and stones. The cells are contiguous, o\al, with a blunt 
conical process at the summit of each. It often covers the stem 
of the older specimens of this Sertularia. Both the Sertularia 
and Tubularia are much infested with several species of Vorti- 
jcelloe, among which the beautiful F. polypina is preeminently 
conspicuous. A small species of Coryna has likewise presented 
itself, whose characters have not as yet been sufficiently ascer- 
tained 
The preceding description agrees in so many particulars with 
the characters which Pallas gives of his Sertularia gelatinosa, 
that I have adopted his trivial name without any suspicion* 
T’here is, however, one point of difference on which it is neces- 
sary to make a few remarks. Pallas, when describing his spe- 
cies, says (Elenchus Zoophytorum, p. 117.) of the mouth of 
the denticle, ‘‘ margine eleganter crenato,” while, in the species 
which I have described, the margin is plain and even. But, 
from the variety of aspects in which I have viewed the denticles, 
in reference to the structure of their mouth, and having used diffe- 
rent magnifying powers, I am satisfied that their margins are even, 
and suspect that Pallas has been misled by some appearances 
which likewise presented themselves to me in the course of ob- 
servation. The polype frequently retreats into the denticle 
-only imperfectly, leaving the extremities of the tentacula visible 
above the margin, thereby giving it the appearance exhibited 
by the S. volubilis,- in Ellis’s Cor. Tab. xiv. f. A. It is only 
when pricked with a needle, or left without water for a short time, 
that it retreats completely within the cell, and permits the margin 
to be viewed distinctly ; precautions which, it is probable, Pallas 
-did not adopt. Besides, the numerous vorticellae which occupy 
the surface and margins of the denticles, give to the latter in 
certain combinations a crenated appearance. 
Upon comparing the characters which this Sertularia presents, 
with the different figures in Ellis’s Corallines, I am led to con- 
isider Tab. xii. f. c C, and Tab. xxxviii. fig. 3., as representa- 
* In the month of August 1817, I observed two species of Corynse alive in the 
sea at the Isle of May, the C. squamata, and C. glandulosa of Lamarck. Professor 
Jameson found the former species in the Zetland Islands in 1798; and I have 
specimens which I picked up at Abercorn in 18(K>. 
