286 Rafinesque on a fossil Medusa. 
well known that the animals of that tribe are of a soft gela- 
tinous substance and structure, they do not leave any exuviz 
after their death, and they are very easily destroyed by the 
contact of any hard substance, whence it is no wonder that 
their fossil remains are so rare: yet in the specimen under 
consideration, the animal appears quite perfect, and is em- 
bedded in a crystallized limestone ; the mode of its fossili- 
zation is therefore very singular. We must either suppose 
that this extinct species was of a harder cartilaginous sub- 
stance, or that the liquid in which it was swimming or floating, 
was coagulated at once: it even appears probable to me that 
both circumstances may have occurred, since the specimen 
is in its proper natural position, and not in the least com- 
pressed nor altered; but the whole of it is changed into a 
similar stone to that which surrounds it: the animal howev- 
er is become rather silicious as usual with fossil mollusca 
or polyps. 
ee | Genus Trianisites.—(See the engraved figure.) 
Generic definition.—Body with three unequal peduncles 
or appendages underneath, the middle one with a mouth or 
opening at the extremity, surrounded by two fascicles of 
short tentacula. Back simple, not ombrelled. 
renertc observations.—The generic name derives from 
Greek words meaning, three unequal appendages. In the 
natural arrangement this genus will belong to the real family 
medusa, and to the sub-family branchypia, having peduncles 
or appendages underneath and no wing nor bladder on the 
back, next to the genus pelasgia of Peron and Lesueur; but 
it differs from it, and indeed from any other of that tribe, 
by having a sort of trifid body, and the tentacula only near 
the mouth. The following species is the type of the genus. 
T; ee ites Cliffordi. 
_ Specific definition —Back subconical and subacute, axil- 
las obtuse and unequal, peduncles compressed tran srsally 
ad eaten PSse ransve 
obtuse, the shortest larger, the longer one smaller and op- 
sed to it, the middle one nearly as long, extremity fim- 
ed by the tentacula. | ; 3 
