AMERICAN COLEOPTERA. 257 



Synopsis of tbe 9IO]VOT09IID^ of the United States. 



BY GEORGE H. HORN, M. D. 



This family contains a small number of genera in which the anterior 

 coxae are small and round, without trochanters, their cavities widely 

 closed behind. Middle coxae small, round, closed by the mesosternal 

 epimera. Posterior coxae transversely oval. Abdomen with five free 

 ventral segments, the first and fifth elongated, the intermediate three 

 shorter and equal. Tarsi three-jointed, last joint longer than the 

 others united. Claws simple. Antennae ten-jointed, club of either 

 one or two joints. Maxillae bilobed. Labrum almost entirely con- 

 cealed by the epistoma. Elytra truncate, pygidium exposed. 



The males have a small additional segment as in the Rhizophagini. 



The differences between the genera composing this family and the 

 Lathridiidae seem to be narrowed down to — elytra truncate and 

 pygidium exposed. I am unable to find that any more definite char- 

 acters have been given by authors, and my studies of the genera of 

 Lathridiidae as restricted by Dr. Leconte are not so thorough as to 

 warrant any definite expression of opinion, but I am inclined to adopt 

 the views of Lacordaire and the Catalogus Gemm. et Har., where the 

 genera here included are placed among the Lathridiidae. A further 

 discussion of this subject is deferred until an opportunity is afforded 

 for revising Lathridius and its closely allied genera. 



It is surprising what differences of opinion prevail in the books 

 regarding the number of the tarsal joints. Lacordaire and Erichson 

 say three, Aube and Motschulsky four, Redtenbacher 3 — 4 — 4, Leconte 

 five. My own observations are in accord with Erichson. 



The following arrangement of the genera is proposed : 



Head slightly i)rolonged behind the eyes, then suddenly constricted 2. 



Head parallel behind the eyes, not at all constricted 5. 



2. — Intercoxal process of abdomen broad, feebly rounded in front 3. 



Intercoxal process triangular, acute 4. 



3. — Terminal joint of antennae suddenly broader, joint nine not wider than 



eight MONOTOMA. 



Last two joints enlarged. 



Ninth joint as wide as the tenth. Elytra irregularly punctured. 



PHYCONOMUS. 

 Ninth joint not as wide as tenth. Elytra punctured in striae. 



HESPEROB^NUS. 



4. — Ninth joint as wide as tenth. Elytra punctured in striae EUROPS. 



5. — Last joint of antennae suddenly enlarged, ninth not wider than eighth. 

 Elytra punctured in striae BACTRIDIUM. 



TRANS. AMER. ENT. SOC. VII. (33) JUNE, 1879. 



