of the Amazon Valley. 213 



cavity between the antennse : mouth projecting ; mandibles long 

 and flattened : eyes wide apart. Antennse slightly hairy, never 

 fringed beneath as in Oreodera ; the basal joint always pyriform 

 clavate, smooth, considerably shorter than the third. Thorax 

 with a simple large conical tubercle on each side, generally 

 ending in a spine. Femora strongly clavate; tarsi moderate, 

 claw-joint short ; fore tarsi in the d broadly dilated and ciliated. 

 The above are the only characters that I find tolerably con- 

 stant in the thirty-eight species which I have examined. The 

 forms are very variable in most of the parts of structure from 

 which generic characters are derivable, and exemplify well the 

 difficulties which the Longicorn family ofiers to the classifier. 

 No definition has yet been given founded on a large number of 

 species. That of Leconte (" Attempt to classify, &c.," Journ. Ac. 

 N. Sc. Philad. ii. n. s.) is probably the best j but, relating only 

 to the two or three North American species, it is not applicable 

 generally. The rounded outline of the anterior acetabula, which 

 he gives as a character of the section to which Acanthoderes be- 

 longs, is very variable. In A. varius, the European species 

 which may be considered typical of the genus, they are angu- 

 lated ; in other species the acetabular sutures are gaping along 

 their whole length ; in a few, however, they are closed. Although 

 they differ in species otherwise closely allied, yet they are more 

 constantly closed in those which approach Steirastoma. The 

 head is generally plane in front, the muzzle prolonged consider- 

 ably below the eyes, the lower lobe of the latter being very 

 small ; in some few species, however, the eyes are rather more 

 voluminous below the antennae, thus reducing the breadth of 

 the forehead and the length of the muzzle. The palpi are always 

 elongated, with the terminal joint obtusely pointed. The ligula 

 has its sides dilated and rounded ; the lobes, however, are widely 

 divergent in some species {A. thoracicus), and nearly united to 

 their tips in others [A. bivitta). The antennse are very variable 

 in length, thickness, and shape of the joints, being in some 

 species no longer than the body, in others twice the length : the 

 third joint is generally very long, and the fourth considerably 

 longer than any of the following ; sometimes the two are as long 

 as the remaining taken together; both are generally filiform, 

 with a longitudinal furrow above, but they are occasionally di- 

 lated and produced beneath at their apices, and in a few aber- 

 rant species furnished with tufts of hairs : the terminal joints 

 are generally filiform, sometimes short, thickened, and ciliated 

 in the <J , and sometimes dilated and serriform in both sexes. 

 The thorax has the lateral tubercles, in rare instances, very 

 obtuse; the dorsal surface is uneven, sometimes tuberculated, 

 occasionally furnished with three very prominent tubercles, but 



