EXTERNAL ANATOMY OF INSECTS. 443 
the middle*. In other tribes the upper valve is some- 
times linear and rounded at the apex, and the lower 
truncated, as in Goerius olens®; sometimes the upper 
one is truncated or obtise, and the lower acute, as in 
Trogosita and Parnus*. In Ptinus, another tribe of 
beetles, before noticed as injurious to our museums 4, 
the reverse of this takes place, the upper-lobe, which is 
the smallest and shortest, being acute, and the lower 
truncated *«. In Blaps both are acute'. In Rhipiphorus 
and Scolytus the lobes are nearly obsolete. The lower 
lobe is bifid in Languria, a North American genus of 
beetles, so as to give the maxilla the appearance of three 
lobes§; and in Erotylus, a South American one, the 
upper is triangular": it is often oblong, quadrangular, 
linear, &c. in others.—In those that have only one 
lobe, or a very minute one, the shape also varies. In 
Gyrinus, the beetle that whirls round and round on the 
surface of every pool, there is, as we learn from Mr. 
Curtis', a modification of the palpiform upper lobe, 
which distinguishes the Predaceous Coleoptera, which 
in this genus is exarticulate and spiniform. In the 
larger species (G. americanus ? §c.), according to La- 
treille*, there is a further aberration from this type, as 
the lobe in them is obsolete. Olivier overlooked the 
* Clairv. Ent. Helvet. ii. t. xxiv. f. super. 6. 
> Prare XXVI. Fic. 11. 
© Oliv. Ins. no. 19. Trogosita. t. 1. f. d. no. 41. bis. Dryops. t. 1. 
Bie 4 See above, Vot. I. p. 240. 
Oliv. Ins. no. 17. Ptinus. t.i. f. 1. ¢. 
Ibid. no. 60. Blaps. t. i. f. 2. ¢. 
° Ibid. no. 88. Languria. t. 1. f. 2 
Ibid. no. 89, Erotylus. t. ii. ra Ca 
i Brit. Ent. t, 79. k N. Dict. ad’ Hist. Nat. xiv. 91. 
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