CRUSTACEA. 
272 
is terminated by two long liairs. The lateral expansion merely ap- 
pears to be an excessive developement of the fourth and last ring of 
the thorax. Within we may perceive two kinds of entrails origi- 
nating from the median line of the body, which may be considered as 
Cceca or divisions of the intestinal canal in a state of hernia. They 
are endowed with a very decided peristaltic motion. We have seen 
that the stomach of the Arguli also exhibits two caeca, Avhich ramify 
in the wings of their shell, and it is possible that these thoracic ex- 
pansions of the Nicothoes may be two analogous lobes *. 
Nicothoe astaci, Aud. and Edw. Ann. des Sc. Nat., 1826, 
XLIX, 1,9. The only species known; it is about half a line 
long and three lines broad, the thoracic enlargement included. 
It is rose-coloured, paler on the oviperous sacs; the expansions 
yellowish. It adheres closely to the branchiae of the Lobster, 
and penetrates deeply between the filaments of those organs. It 
is only found in small numbers, and on a few individuals. All 
the Nicothoes observed by these two naturalists were furnished 
Avith ovaries ; it is probable that previously to fixing themselves 
on the branchiae of the Lobster, and before their thoracic lobes 
have acquired their ordinary developement, they can SAvim ; that 
developement, as is the case Avith the body of the Ixodes, may 
be the result of superabundant nutrition. 
TRILOBITES. 
According to Brongniart and various other naturalists, it is in the 
vicinity of the Liinuli and other Entomostraca Avith numerous feet, 
that Ave should place these singular fossil animals, originally con- 
founded under the common name of Entomolithus paradoxus, and 
noAV designated by that of Trilobites, of Avhich an excellent mono- 
graph, enriched Avith good lithographic figures, has been published 
by that gentleman f. By this hypothesis Ave have to admit as a 
positive or at least highly probable fact, the existence of locomotive 
organs, although, notAvithstanding the most careful investigation, no 
vestige of them has been discovered J. Presuming, on the contrary, 
* 111 this case, the genus may be approximated to the preceding one. 
f M. Eudes Deslongchamps, professor of the University of Caen, Count Ra- 
soumowski, M. Dalman and other savans have since published new observations on 
these fossils. M. Victor Audouin, zealously advocating the opinion of Brongniart, 
has contested that published by me, in which I approximate them to Chiton. The 
great difficulty was to prove the existence of feet, and this he has not done. The 
application of his theory of the thorax of Insects to the Trilobites, appears to me 
so much the more doubtful, as, according to my view of the matter, the first annuli 
of the abdomen of Insects alone represent the thorax of the Crustacea Decapoda. 
J M. Parkinson (Outlines of Oryctology) thinks he has perceived them, and 
suspects that they are unguiculated. See also the Entomostracile gramtlcux, Brongn., 
Trilob., Ill, 6, Ann. des Sc. Nat. tome XV. 
