upon the Thyscnnira, 91 



to be observed that the name of the order is invariably misspelt 

 Thrysanura. 



We are indebted to Latreille for a very valuable memoir upon this 

 order, published last year in the first volume of the 'Nouvelles Annales 

 du Museum d'Histoire Naturelle', in which the most ample details 

 are given relative to the structure of the different groups. He has 

 not, hovi^ever, given descriptions of the numerous species of the Po- 

 durida. This blank has in part been fiUed up by Mr. Templeton. 



It is to be regretted that even in this small group confusion has 

 arisen in the nomenclature of the genera, resulting, as is so repeat- 

 edly the case, from proper regard being neglected to be paid to those 

 particular species which constitute the types of the genera as origi- 

 nally constituted. 



It is evident that the Forbicina of Aldrovandus was intended for the 

 Lepisma saccharina of Linnaeus. Geoffrey, although aware of this, 

 sunk the Linnsean generic name Lepisma, and adopted that of For- 

 bicina, adding a second species, la Forbicitie cylindriqiie. Latreille, 

 adopting the Linnsean name of Lepisma for the saccharina, properly 

 considered that as Forbicina was evidently synonymous therewith, it 

 would be imjjroper to employ it even for Geoffroy's second species, 

 to which he accordingly gave the name of MachiUs. He, however, 

 referred Geoffroy's species to the Lepisma jwlypoda of Linnaeus, a step 

 which, from the description of Dr. Leach, would appear to be incor- 

 rect. The last-named author, by sinking Latreille's name of Ma- 

 chilis and adopting Geoffroy's Forbicina, acted, as it seems to me, 

 neither with correctness nor respect to his friend Latreille. He de- 

 scribed the genus as having the antennae shorter than the body, 

 giving the Lepisma polypoda of Linnaeus, and yet gave as synony- 

 mous the cylindrique of Geoffroy, who expressly says that these 

 organs are longer than the body. 



He likewise established another genus, Petrobius, upon a species 

 found upon our coasts. 



Latreille, however, in the memoir above noticed, considered the 

 latter as not sufficiently distinguished from the other species of 

 MachiUs, which he divided into two sections: 1st, with antennae 

 longer than the body, including the Forbicine cylindrique of Geoffroy, 

 under the new name of MachiUs annulicornis , and the Petrobius mari- 

 timus of Leach ; and, 2ndly, those with antennae shorter than the 

 body, including the species figured in his ' Genera Crustaceorum', 

 and which he regards as the Forbicina polypoda of Leach, but doubts 

 whether it be the polypoda of Linnaeus*. 



* I had hoped to have been enabled to clear up this doubt by an examination of 

 the Linnaean specimens ; but notwithstanding a careful and repeated search through 



