TRANSACTIONS OT THE SECTIONS. 
603 
On an hitherto undescribed Modification of the Respiratory 
Organs of certain Crustacea. By J. O. Westwood, 
F.L.S. &c. 
The object of this memoir was to illustrate the principal cha¬ 
racters of an animal obtained from Shetland, of the genus Pra¬ 
niza , included among the Malacostraca edriophthalma of Leach; 
and especially to furnish a description of some peculiarities in 
its respiratory apparatus, as compared with the variations of 
that system already known in the several groups of the typical 
Malacostraca. The author, after giving an account of the 
history of the species, and of many parts of the organization 
of the animal, proceeded to describe more particularly the ab¬ 
domen and the respiratory appendages beneath it. 
The branchial organs of Isopodous Crustacea resemble those 
above described as found in the genus Praniza, by their plate¬ 
like form and the number of their pairs ; but they are entirely, 
or in a great measure, covered by the large basal pair resulting 
from the slight development of the abdomen; those of the Am- 
pliipoda are exposed as in Praniza, but acquire a linear form ; 
while those of Stomapoda, equally exposed, are found to con¬ 
sist of bundles of filaments. The group of Stomapoda belong¬ 
ing to the Podophthalmic division of Crustacea, whilst Praniza, 
with the Isopoda and Amphipoda, forms part of the division 
Edriophthalma, it follows evidently that it is between the Iso¬ 
poda and Amphipoda that the true place of Praniza is to be 
sought in a natural distribution; and here the author places 
it in a small osculant group: thus reconciling the conflicting 
opinions of several authors, by whom it was classed in one or 
other of these groups, according to their peculiar views of its 
affinities. 
The abdomen of the animal is about half the length of the 
thorax, and formed of five depressed transverse joints of equal 
breadth, but narrower than the thorax; the lateral caudal plates 
are representations of the sixth abdominal segment, as in the 
lobster; and the seventh or terminal segment is represented by 
an elongate conic plate, forming with the lateral ones a quinque- 
partite caudal swimming organ, as in the shrimps. 
The subabdominal appendages were found to consist of flat, 
very delicate, suboval, deeply ciliated, membranaceous plates, 
two pairs to every one of the five abdominal segments, inserted 
in pairs at each side of the joints beneath. These organs are 
of an equal size, except those upon the fifth segment, which 
are very slightly larger than the preceding. They are consider¬ 
ably smaller than the joints to which they are respectively at- 
