EXTERNAL ANATOMY OF INSECTS. 683 
Sigara and Naucoris 1:2:2; in anew subgenus between 
Belostoma and Naucoris (Xiphostoma K. MS.), brought 
by Dr. Bigsby from Canada, 3: 2:2: in the Lepidoptera 
the butterflies called tetrapi (Vanessa, &c.) may be ex- 
pressed by 1:5:5. Amongst the Aptera and Arachnida 
there are three remarkable genera, which if their pedi- 
palps are included may be deemed Heteromerous. I 
mean Phrynus, Thelyphonus, and Galeodes ;—in the 
former the numbers will be *: 4: 4:4, the asterisk denot- 
ing more than ten; in the second, 8:4:4:4.; and in 
Galeodes (in which the first pair of pedipalps are not 
chelate, the mandibles performing their office) the 
numbers are 1:1:3:3:3.? 
Tetramerous insects are those in which all the farsz 
consist of four joints; these in the Coleoptera are next in 
number to the pentamerous—indeed a very large propor- 
tion of them strictly speaking are really of the latter 
description, since in Linné’s four great genera, Curculio, 
Cerambyx, Chrysomela, and Cassida and some others, 
the claw-joint (ungula) consists of ¢wo articulations, one 
very short, forming merely the ball at its base >, which 
inosculates in the socket of the preceding joint, and the 
other constituting the remainder: if you carefully sepa- 
rate these two pieces, you will find that the last inoscu- 
lates in the summit of the ball, and is moved by appro- 
priate muscles*. This structure probably permits the 
« These three genera appear really to have only six legs, since the 
pedipalps or maxillary legs are not armed with claws, while the 
real representatives of the legs, or three last pair, are so distin- 
guished. In Phrynus and Thelyphonus the anterior pair are chelate; 
but in Galeodes they are pediform, as in the Avaneida, and the great 
chelez are the mandibles. > Prate XXVI. Fic. 47, 48. d*. 
© Ibid, Fie. 49. s*. a. 
* 
