178 PROC. ENT. SOC. WASH., VOL. 23, NO. 8, NOVEMBER, 1921 



However, when the skin is examined from the interior, the four 

 tergal areas are to be found (Plate XIV, fig. 1). The anterior 

 area is a constricted, unarmed, narrow band partly (or entirely) 

 covered by the head and connects the head with the first area 

 of the prothorax which is visible from the exterior (B). This 

 unarmed band I have considered as the aborted first area (A) 

 of the prothorax thereby completing that segment. 



Thus we see, that to limit the segment of a larva of Pteronidea 

 ribesii in any other manner than that described above makes it 

 necessary to (1) ignore the neck-like membrane of the prothorax 

 or to explain its presence by deriving it from the head or to con- 

 sider it as a distinct and separate development; (2) to separate 

 as belonging to the ninth abdominal segment a portion of the 

 epiproct which is never a distinct area and which is frequently 

 indistinguishably fused with the remainder of the anal segment 

 or to connect with the anal segment area D of the ninth abdom- 

 inal segment which is never as distinctly separated from the 

 ninth segment as it is from the anal segment; and (3) to consider 

 many small, short, weak muscles as intersegmental, /'. e., arising 

 in one segment and attaching to an infolding in another. 



To summarize: the segment of Pteronidea ribesii is composed 

 tergally of four areas and begins with the area preceding that 

 above the spiracle. These areas are here designated by the 

 letters A, B, C and D with the anterior being known as A. The 

 first three (A, B, and C) of these areas are ornamented with 

 spots and hairs while the posterior one (D) is plain and entirely 

 without spots or hairs. That other sawfly larvae agree with 

 this limitation and composition of a segment may be demon- 

 strated by the following examples: 



Nediprion lecontei (Plate XIV, fig. 4). The thorax and tenth 

 abdominal segment of Neodiprion lecontei is practically of the 

 same construction as Pteronidea ribesii but in the first nine 

 abdominal segments area C is twice subdivided forming three 

 subareas (Cl, C2, C3) of which only the middle one (C2) is 

 ornamented. Hence the construction of the tergum of Neodi- 

 prion lecontei is: Thorax A, B, C and D. Abdomen (urites 

 1-9) A, B, Cl, C2, C3 and D; (urite 10) epiproct. 



Arge. (Plate XIV, fig. 6.) In the larvae belonging to the 

 genus Arge the thoracic and abdominal (1-9) segments appear 

 to consist dorsally of only three areas (A, B and C). The fourth 

 area (D) is present however, but infolded under C. This may 

 easily be demonstrated by splitting a larva longitudinally along 

 the back, or by injecting a living larva with alcohol, which ex- 

 pands the body. 



Cimbex. (Plate XIV, fig. 7.) The larva of Cimbex ameri- 

 cana is in respect to A, C, D similar to Neodiprion lecontei but 

 B is divided Bl and B2, in both the thorax and the abdomen. 

 The construction of the tergum of this species is: Thorax A, 



