114 Proceedings of the 



avoid the conclusion that they belong to the same species. The 

 differences that exist other than the broad thorax are very trifling. 

 The antenna? of grandicollis are perhaps a trifle thinner and not 

 so dark in the middle as in the generality of tristis, and the ter- 

 minal joint is usually not paler than the rest of the club. But 

 these are all variable items in tristis itself. I have specimens 

 with their antenna? in every respect to the most minute parti- 

 cular the same in both kinds. The only other discrepancy is, 

 that the slight sinuation on the posterior margin of the thorax of 

 tristis seems wanting in grandicollis. In a word, the only per- 

 manent difference is in the form of the thorax, which, in the face 

 of the circumstances I have adverted to, does not in this instance 

 appear to me a sufficient ground for constituting it a different 

 species. 



Another curious confirmation of this view is, that similar 

 variations in the form of the thorax take place in C. chrysome- 

 loides. In fact, I possess specimens of the latter having exactly 

 the form of tristis; the sole difference being that they are larger; 

 the thorax is more coarsely granulated, its pubescence darker ; 

 the elytra more rounded and not so acuminate at the apex, their 

 bloom also is ash-grey instead of purplish, their base is black 

 instead of brownish, and the yellow hairs at the base are wanting. 

 The antenna? are thicker and darker and the last joint is longer. 

 These particulars serve to show that it is not tristis; and in 

 addition these varieties are found mixed with large numbers of 

 the normal form of chrysomeloides. For instance, among about 

 200 specimens of chrysomeloides which my friend Mr. Bates re- 

 cently sent me, all taken together at one time, I found three or 

 four with the form of tristis ; also a specimen or two having in 

 like manner exactly the form of grandicollis, but with the elytra 

 not as in the variety of tristis bearing that name, but as in chry- 

 someloides ; the antenna? are thicker and darker, but there is no 

 other difference in the relative proportions, except in the last 

 joint, which is not long, as it is in chrysomeloides. Further, there 

 were a few specimens in the same lot having the shorter form 

 and more acuminate elytra of rotundicollis ; and lastly, there were 

 examples having the form of the thorax of nigrita. The result 

 to which I have come therefore is, that similar variations in form 

 exist both in C. tristis and C. chrysomeloides ; that as we have a 

 variety of the former with a broad thorax (C. tristis var. grandi- 

 collis), we have also a variety of the latter of like form (C. chry- 

 someloides var. grandicollis). In like manner of each we have 

 C. tristis var. rotundicollis and C. chrysomeloides var. rotundi- 

 collis, and C. tristis var. nigrita and C. chrysomeloides var. nigrita. 

 We have a var. of chrysomeloides like tristis (C. chrysomeloides var. 



