46 OTSTER-SSELL BAEK-LOUSE. 



Though opposed, as a general principle, to the disposition exhibited by many modern 

 authors, to the excessive sub-division of genera under distinct sub-generic titles, yet 

 the name Mytilasp'is is so happily expressive of the form of these insects, that I have 

 thought it best to adopt this term for the present species, and also for that found on the 

 leaf of the pine, treated of at the close of this report. 



The specific name, conchiformu, was originally given by Gmelin to a European species, 

 the history of which is a good deal confused. It appears to have been originally applied 

 to a species found on the elm; but Dr. Shaw, as quoted by Dr. Harris, states that it is 

 abundant on the apple trees in England, and Mr. Kirby and Mr. Rennie add that it i 8 

 also found on the currant-bush, all of which, as respects its habit, goes to identify that 

 species with our Northern Apple-tree Bark-louse. Moreover the description given by 

 M. Signoret of the M. coneliifiinhi", as found upon the elm, corresponds, in all its more 

 obvious characters at least, to our apple-tree species; but on the other hand it is a re- 

 markable fact, and one which tends to throw considerable doubt upon the identity of the 

 species, that the M. con< hlformin oi Europe seems to be generally admitted as peculiarly 

 the Bark-louse of the elm, whereas our American species, so far at least as I have been 

 able to observe, is never found upon the elm in this country. The force of this fact, 

 however, as affording an argument against the identity of the two species, is considerably 

 weakened by the occurrence of our species on the currant-bush, and very abundantly on 

 the Persian Lilach — plants as far removed as the elm in their natural relations to the 

 apple tree. This question of identity can be definitely settled only by the actual com- 

 parison of specimens obtained from these several sources. 



But here follows some interesting statements appertaining to this subject. M. Signoret, 

 writing, we may presume, more especially from observations made in the latitude of 

 France, speaks oi the M. conchiformis as being exclusively an inhabitant of the elm, and 

 described another species, under the name of M. pomorum of Bouche, as being the spe- 

 cies which infests the apple tree. Upon referring to this description and the figure illus- 

 trating it, we find it to be quite different from the species that infests the apple tree in 

 this country. Besides some minute particulars, it is described as having a blackish- 

 brown scale with a white apical border, whereas our species is of a uniform ashen-brown 

 color, like the bark of the tree, and still more remarkable as having red eggs, whilst the 

 eggs of the American concMformis are invariably white. Neither can it be identified 

 with the Harris's Bark-louse of this country, which, though it resembles the other in 

 having red eggs, is of different form and belongs to a different sub-genus. From all 

 this we draw the interesting conclusion that in Europe, as in this country, there are two 

 species of Bark-louse, a more Northern and a more Southern species, which inhabit the 

 apple-tree. 



