CALIFORNIA ACADEMY OF SCIENCES. 3 



bust in Metaxyoclonta — and scarcely perceptibly incrassate. 

 The nftli abdominal segment is almost invariably equal in 

 length to the third and fourth together. The labrum differs 

 throughout, and is, in conjunction with the relative length 

 of the first joint of the posterior tarsi, made the principal 

 basis of generic subdivision. It is singular, however, and 

 a strong proof of the validity of the genera, that these two 

 fundamental characters are accompanied by other very rad- 

 ical differences in many of the most important parts of the 

 body, as well as in completely radical differences in the na- 

 ture of the male sexual modifications; these are described in 

 the table of genera given below. 



The genera Stilicus, Scopseus, Orus, etc., should pre- 

 cede those here given in a systematic arrangement of the 

 Psederi, and are distinguished from them by tlieii' very 

 strongly dilated third maxillary palpal joint. 



San Francisco, Jan. 1st, 18S6. 



Note 1.— In estimating the order of the abdominal segments in the follow- 

 ing pages, the numbers refer to visible segments only. 



Note 2. — Separate diaguoses of the various species are not given at present. 

 as this paper is simply intended as the forerunner of a more general one upon 

 onr Paederini. 



GENERIC DEFINITIONS. 



Head slightly narrower than the prothorax, sides parallel; eyes moderate 

 in size; labrum 4-dentate, the teeth being rather prominent, acute and nearly 

 equi-distant. Prothorax quadrate; sides parallel or very slightly narrowed 

 from apex to base. Elytra much longer than the prothorax. First joint of 

 the posterior tarsi as long as the next two together, or nearly so. Male sex- 

 ual characters very simple; fifth segment not modified, sixth narrow, with a 



small simple sinuation at the apex G-enus Caloderma. 



Pronotum longitudinally rugulose Species 1 — 3. 



Pronotum finely and generally very densely punctate Species 4 — 8. 



Head rather large, slightly wider than the prothorax; eyes, very small; la- 

 bmm with a very small deep median emargination, slightly wider than deep, 

 immediately adjoining which there are on each side two approximate and ex- 

 ceedingly minute acute teeth. Prothorax with the sides convergent pos- 



