190 Prof. J. O. Westwood's Notes on the genus 



filaments, Latreille added in his characters of the genus 

 (to which he ^2iVQ\hQn^mQ of Prosopistoma): " Abdomen 

 en forme de petite queue, compose de quatre segments, 

 dont le dernier applati, presque semi-circulaire, portant des 

 filets barbus branchiaux et retractiles,^'' on the authority 

 of Geoffrey's original description, and which, his young 

 friend Audouin had affirmed, existed in the Madagascar 

 insect, "retires" within the terminal segment of the body. 

 "■ II est probable," adds Latreille, " que ces organes servent 

 a la natation et a la respiration et font 1' office des branchies ; 

 car Geoffroy a observe que I'espece, par lui decrite, agite 

 precipitamment la queue: ces Crustaces n'ont d'ailleurs 

 aucun autre appendice que Ton puisse regarder comme 

 propre a cette derniere fonction." 



Latreille terminates his observations on his new genus 

 with the remark, " Ce genre semble devoir former a lui 

 seul une famille particuliere, terminant la division des 

 Crustaces dentes ou munis de machoires. Cependant, 

 jusqu'a ce que de nouvelles recherches nous aient parfaite- 

 ment devoile I'organisation buccale, et que nous soyons 

 assures qu'il n'existe point de siphon, nous suspendrons 

 notre jugement." Lastly, Latreille gave the specific name 

 of Pr. ^^ariegatum to the Madagascar insect, and that of 

 Pr. punctifrons to Geoffroy's French species. 



In 1872, appeared in the Annales des Sciences Natu- 

 relles, 5 Ser., Zool., t. xvi. Art. 7, a memoir by Messrs. 

 N. & E. Joly, entitled, "Etudes sur le pretendu Crustace, 

 au sujet duquel Latreille a cree le genre Prosopistoma, 

 et qui n'est autre chose qu'un veritable insecte hexapode;" 

 " un veritable insecte, encore incompletement developpe, 

 encore dans cet etat que les naturalistes Anglais designent 

 sous la denomination heureuse, mais un pen elastique, de 

 ' an immature condition,' une larve aquatique d'Epheme- 

 rine." 



This unexpected conclusion was arrived at by these 

 authors in consequence of one of them having rediscovered 

 it in September, 1868, in the basin of the Garonne, near 

 the Island of Grands Ramiers, and thus being able to 

 make a complete examination of the more important 

 internal organs of the creature than could be obtained 

 from dried individuals or from the incomplete description 

 of Geoffroy. 



The most important of the structures observed by these 

 authors is the discovery of a tracheal system of respiration, 

 announced as follows : " S'il pouvait rester encore quelques 



