430 
CRUSTACEA. 
Fi§;. 13. — Caprella phasma. 
Leptomera, Latr, {Proto, Leach), has fourteen complete legs (including the pair attached to the head), forming 
a regular series. In some of them (as in Gammarus pedatus, Muller, forming the type of the restricted genus 
Leptomera) all the legs (except the two anterior) are furnished with a basal vesicle, whilst in the others {Cancer 
pedatus, Montague, being the type of Leach’s Proto) these appendages exist only at the base of the second and 
four following legs. 
Naupredia, Latr., has ten legs in a continuous series, the second and two following pairs having a vesicular 
body at the base. The typical species found on the French coast appears to me to be undescribed. 
Caprella, Lamarck, have also only ten legs, but the series is interrupted; the second and following 
segments being destitute of legs, but each is 
furnished with two vesicular bodies. Type, Squilla 
lobata, Muller. 
[Dr. Johnston has published a monograph of 
the British species of this section in the eighth 
volume of the Magazine of Natural History, and 
Dr. Templeton and M. Guerin have respectively 
described various additional species of this curi- 
ous group.] 
The other Loemodipoda, forming a second section (Ovalia, Latr.), have the body oval, with the seg- 
ments transverse ; the terminal filament of the antenn® appears to be inarticulated. The legs are short, 
or of only moderate length ; those of the second and third segments are imperfect, and terminated by a 
long cylindrical joint without terminal hooks ; they have at the base an elongated vesicular body. 
These Loemodipoda form the subgenus — 
Cyamus, Latr. {Larunda, Leach), of which 1 have seen three species, all of which live 
upon Cetacea, and of which the commonest {Oniscus Ceti, Linn.) is also found upon the 
Mackerel. The fishermen call it the whale-louse. Another species, closely allied, was 
brought home by Delalande, in his voyage to the Cape of Good Hope. The third, which is 
much smaller, is found upon the Cetacea of the Indian seas. 
[M. Roussel de Vauz^me has published a very complete and interesting memoir upon 
this singular genus in the Annates des Sciences Naturelles for May, 1834, describing three 
species living upon Whales of the Southern Ocean, and also observed their respective 
habits. Sometimes these creatures are so abundant on the Whales that the individuals 
they infest may be easily recognized at a considerable distance by the white colour these 
parasites impart to them. When removed, the surface of the body of the Whale is found 
to be deprived of its epidermis. C. ovalis and gracilis are stationary, being found in great 
numbers agglomerated upon the corneous prominences of Bal<ena mysticetus. C. erraticus is, however, organ- 
ized for its wandering habits, being of a slender form, and with larger legs, serving for prehension. The young 
ones appear with all the characters of their kind, only the head is rather large, and the supposed branchial appen- 
dages, instead of being long and slender, are short and somewhat globose.] 
Fig. 14. — Cyamus 
Balaaiiarum. 
THE FIFTH ORDER OF CRUSTACEA, 
ISOPODA,— 
Or the Polygonata of Fabricius, (after the removal of the genus Monoculus) is allied to the 
Loemodipoda in the absence of palpi to the mandibles, but is separated from them in other 
respects. The two fore-legs are not attached to the head, but to a distinct segment, as are the 
following feet. These limbs are always fourteen in number, hooked at the tip, without any ; 
vesicular appendage at the base. The under-side of the tail is furnished with very distinct ' | 
appendages, in the form of plates or vesicular bags, of which the two anterior and exterior : 
ordinarily cover, either entirely or for the most part, the others. The body is generally ( 
flattened, or broader than deep. The mouth is composed of the same pieces as in the pre-| 
ceding; (see the general remarks on the Malacostraca) ; but here, those which correspond with^ 
the two superior foot-jaws of the Decapods present, even more strongly than in those? 
Crustacea, the appearance of a lower lip, terminated by two palpi. The intermediate pair of j 
antennae is obsolete in the terminal species in the order, which are terrestrial in their habits,| 
and which [consequently] differ from the rest in respect to their respiratory apparatus. 
M. V. Audouin and M. Edwards have given {Ann. des Sciences Nat., 1827) some interesting] 
