272 CRUSTACEA. 



is terminated by two long hairs. 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 

 caeca 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 cseca, which 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 

 with 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 swim ; that 

 developement, as is the case with the body of the Ixodes, may 

 be the result of superabundant nutrition. 



TRILOBITES. 



According to Brongniart and variovis other naturalists, it is in the 

 vicinity of the Limuli and other Entomostraca with numerous feet, 

 that we should place these singular fossil animals, originally con- 

 founded under the common name of Entomolithus paradoxus, and 

 now designated by that of Trilobites, of which an excellent mono- 

 graph, enriched with good lithographic figures, has been published 

 by that gentleman f. By this hypothesis we have to admit as a 

 positive or at least highly probable fact, the existence of locomotive 

 organs, although, notwithstanding the most careful investigation, no 

 vestige of them has been discovered \. Presuming, on the contrary, 



* In this case, the geuus 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. 



X M. Parkinson (Outlines of Oryctology) thinks he has perceived them, and 

 suspects that they are unguiculated. See also the Entomostracite granuleux, Brongn., 

 Trilob., Ill, 6, Ann. des Sc. Nat. tome XV. 



