358 



Leech and Chandler: Coleoptera 





Fig. 13:52. Elmidoe. a, Dubiraphia sp., adult prosternum; b, 

 Gonielmis dietrichi, adult prosternum; c, Microcylloepus pusillus, 

 adult prosternum; d, Ancyronyx sp., third larval abdominal tergite; 

 e, Stenelmis sp., larval prothorax, ventral; f, Gonielmis dietrichi, 

 left elytra; g, Ordobrevia sp., left elytra; h, Limnius sp., adult; 

 i, Microcylloepus sp., larval pronotum (a,b,d-i, Sanderson, 1953; 

 c, Hinton, 1935). 



Phanocerus, Cylloepus, Neoelmis, Elsianus, Heter- 

 elmis, and Hexacylloepus are mainly Mexican in 

 distribution, extending only into the southern states 

 of the United States. Dubiraphia, Optioservus, and 

 Microcylloepus are found throughout the United States, 

 Optioservus ranging well into Canada and Microcyl- 

 loepus into Mexico. Gonielmis is restricted to the 

 southeastern United States. Stenelmis, Limnius, 

 Macronychus, and Ancyronyx are in the eastern part 

 of the continent. Stenelmis, which contains the largest 

 number of species in the United States, has only one 

 species west of the Rocky Mountains. It is significant 

 that this species, S. calida, is taken in warm springs 

 in Nevada. Cleptelmis, Heterlimnius, Narpus, and 

 Zaitzevia are taken throughout the western United 

 States and into Canada. Lara, Ordobrevia, Ampumixis, 

 Atractelmis, and Rhizelmis are found along the Pacific 

 Coast. 



Taxonomic characters. — Variations in the epipleura 

 and the locking devices for holding it firmly against 

 the ventral abdominal segments to form a rigid air- 

 tight chamber beneath the elytra, serve as useful char- 

 acters in breaking the genera down into related groups. 

 Lara, like the Dryopidae and Limnichidae, has the 

 epipleura broadly reaching the medial suture at the 

 apex of the elytra, but the epipleura is twisted under 

 and applied to the inner side of the elytra near the 

 apex. In the Elmini the epipleura is always tapered to 

 a point and reaches the apex only in group two, con- 

 taining Ordobrevia and Stenelmis (fig. 13:53a). The 

 epipleura is shortened and usually gradually tapered 

 to its apex near the end of the fourth or middle of the 



fifth abdominal segment, in the next composite group 

 (fig. 13:53e). This contains Ampumixis, Atractelmis, 

 Cleptelmis, and Rhizelmis, which are closely related 

 and characterized by the three-segmented maxillary 

 palpi. Also in this group are Macronychus, Ancyronyx, 

 Narpus, and Dubiraphia, which are not closely related 

 to each other or to any other North American genera. 

 Closely related Promoresia, Optioservus, and Heter- 

 limnius, together with the more distantly related 

 Zaitzevia and Limnius, form a group; they have the 

 posterior lateral angle of the fourth abdominal segment 

 produced into a prominent tooth which is usually bent 

 vertically to fit into a slightly widened area near the 

 apex of the shortened epipleura (fig. 13:536). The 

 fifth group contains Elsianus, Neoelmis, Hexacyl- 

 loepus, and Cylloepus; each has a tooth at the middle 

 of the fifth abdominal segment, fitting into a conspic- 

 uously widened area near the apex of the shortened 

 epipleura (fig. 13:53d). Groups two and five have a 

 number of characters in common including the clasping 

 of the epipleura by the basal half of the fifth ab- 

 dominal segment, indicating close ancestral relation- 

 ship. 



The number of segments in the maxillary palpi 

 (3 or 4) is a useful character but difficult to see, 

 especially if the head is retracted. The shape and 

 sculpture of the pronotum, and the sublateral carinae 

 of the pronotum and elytra, characterize many of the 

 genera. Two unrelated genera, Macronychus and 

 Zaitzevia, have the antennal segments reduced in 

 number and the last segment enlarged. Heterlimnius 

 has the antennae ten-segmented in one species and 

 eleven in the other. In a few cases it has been neces- 

 sary to use the distribution of the patches of tomentum 

 on the body or legs. 



Fig, 13:53. Elmidae. a, Stenelmis calida, epipleura and ab- 

 dominal segments; b, Optiservus quadrimaculata, epipleura and 

 abdominal segments; c, Stenelmis sp., odult thorax, dorsal; d, 

 Microcylloepus sp., epipleura and abdominal segments; e, Clep- 

 telmis addenda, epipleura and abdominal segments (Chandler, 

 original). 



