-72 TENTHKEDO AND TENTHREDOPSIS. 



shining, the head and thorax bear white markings, 

 while the blotch is invisible, a character which easily 

 separates it from the other species placed in the genus 

 by Thomson. 



Thomson defines the three genera thus : 



d, Gense distinctse; oculi nempe mandibularum basin hand attin- 



e. Alse superiores cellula lanceolata breviter constricta. 



Synaerema. 



ee. Alse superiores cellula lanceolata nervo transverso brevi 

 perpendicular! instructse ; inferiores cellula humerali 

 breviter appendiculati. Perineura. 



dd. Gense nullse; oculi nempe convergentes mandibularum 

 basin attingentes. Also inferiores cellula humerali haud 

 appendiculata. Mesonotum punctulatum. Tenthredo. 



Besides " instabilis," Thomson includes in Tenth/re* 

 dopsis T. viridis, punctulata, scalaris, gibbosa, and late- 

 ralis. 



I cannot accede to this arrangement. It seems to 

 me that as thus constituted Tenthredopsis is a very 

 artificial arrangement, and that the characters derived 

 from the form of the cheeks and of the slightly appen- 

 diculated posterior wings can scarcely be regarded as 

 of primary importance ; indeed, the latter is a very 

 inconstant character, occurring in very widely sepa- 

 rated species. With T. scalaris, for example, the 

 cellule is, with most of my specimens, scarcely appen- 

 diculated, and in two or three specimens it is com- 

 pletely interstitial. Similarly, the difference between 

 " gense nullge" and gense distinctae" is merely com- 

 parative, and intermediate forms exist. Undoubtedly 

 the gibbosa section forms a connecting link between 

 the "instabilis " group and Tenthredo proper, but with 

 the slight exceptions mentioned above, the species 

 agree very well with Tenthredo. The green species 

 placed in TentJiredopsis by Thomson have so many 

 affinities with olivacea, mesomela, &c., that I do not 

 see how they can be placed apart without violating 

 many affinities. Besides, as thus constituted by Thom- 

 son, Tenthredopsis is a very heterogeneous genus, the 

 two groups composing it instabilis on the one hand, 



