364 



Leech and Chandler: Coleoptera 



broadly oval and very convex, often with the append- 

 ages retractile and fitting into grooves in the body. 

 Some species of Limnichus retract the head into the 

 thorax so that even the eyes are concealed, leaving 

 only the two basal segments of the antennae exposed. 



Relationships. — The adults have many characters 

 in common with the Dryopidae in which Throscinus 

 and Lutrochus were included for many years. The 

 larvae more closely resemble those of the Elmidae. 



Respiration. — The adults are riparian, but the dense 

 hairs on some species suggests that they may be 

 able to submerge with a film of air about their bodies. 

 The larva of Lutrochus has three tufts of retractile, 

 filamentous gills in a caudal chamber similar to those 

 of the elmids. This would indicate that it is truly 

 aquatic. 



Habitat and distribution. — The adults of Limnichus 

 have been taken with Omophronidae and Georyssidae 

 along the margins of streams on wet sand or loam. 

 They may be flushed from their hiding places by 

 throwing water on the bank. Fall (1901:104) reports 

 Limnichus tenuicornis (Casey) from a wet, springy 

 hillside. Throscinus was reported by Fall from mud 

 flats near San Diego which are covered at high tide. 



Key to the Nearetle Genera of Limnichldae 

 Adults 



1. Hypomera with a transverse or oblique ridge (fig. 

 13:57c) LIMNICHINAE 2 



— Hypomera without ridges; Texas to southern California 

 CEPHALOBYRRHINAE .... Throscinus LeConte 1874 



2. Antennae 11-segmented, segments 1-2 large, 3-11 

 pectinate (fig. 13:576); head less retractile, mouth 

 parts and eyes exposed; 1st abdominal sternite not 

 grooved to receive femora and tibiae; eastern U.S. 



Lutrochus Erichson 1847 



— Antennae 10-segmented; 1st abdominal sternite with 

 grooves into which hind femora and tibiae fit 3 



3. Pronotum without cavities on dorsal surface for recep- 

 tion of antennae in repose; antennae slender, without 

 distinct club Limnichus Latreille 1829 



— Pronotum with polished sublateral cavities on dorsal 

 surface to receive antennae in repose; antennae with 

 distinct club Physemus LeConte 1854 



Key to the California Species of Limnichus 

 Adults 



1. Eyes very convex and prominent, rather coarsely 

 faceted and conspicuously visible from above, sides 

 of front above them not acute or cariniform 2 



— Eyes vertical in plane and more or less finely faceted, 

 edges of front of head above them acute and projecting, 

 usually almost concealing them from dorsal view ... 3 



2. Elytral punctures large, very deep, so densely crowded 

 as to be regularly polygonal with very fine separating 

 walls, resembling a honeycomb; southwest U.S.; Tulare, 

 Calaveras, and Yolo counties 



nebulosus LeConte 1879 



— Elytral punctures almost as large and very deep, but 

 impressed, circular, isolated, separated by y% to fully 

 once their own diameters; Mono, Santa Clara, Riverside, 

 San Diego counties perforatus (Casey) 1890 



3. Prosternum not sulcate; Humboldt, San Bernardino 



counties tenuicornis (Casey) 1890 



Prosternum sulcate 4 



4. Elytral punctures minute, feeble, very scattered some- 

 times almost obsolete; southwest U.S.; Riverside 

 County perpolitus (Casey) 1 890 



— Elytral punctures always readily visible, separated 

 by slightly more than, to evidently less than, twice 

 their own diameters 5 



5. Elytral vestiture simple, of subrecumbent, robust, 

 and aciculate hairs 6 



— Elytral vestiture dual, of very small short confusedly 

 matted and densely placed hairs near the surface, 

 and finer, longer, sparser suberect hairs interspersed; 

 southwestern U.S.; San Diego and Riverside counties 

 naviculatus (Casey) 1 890 



6. Smaller species, less than 2 mm. long; elytral pu- 

 bescence sparser, punctures very shallow and separated 



by twice their own widths; California 



calif ornicus LeConte 1879 



— Larger species, more than 2 mm. long; elytral pu- 

 bescence dense, punctures impressed, separated by 

 Vfa times their own widths; southwestern U.S.; Shasta 

 County to Tulare and Sonoma counties to Santa Clara 

 County analis LeConte 1879 



Genus Physemus 

 Adults 





Genus Throscinus 



A single North American species. Length 0.8-1 mm. Form 

 elliptical, strongly convex; color blackish above, reddish 

 below. Elytra shining, finely punctate, with recumbent 

 pubescence; southwestern U.S.; Imperial, Los Angeles 

 counties minutus LeConte 1854 



One species is recorded from California, but the very 

 similar T. politus Casey of the Gulf Coast of Texas 

 and the northwest coast of Mexico should be watched 

 for. It has the third antennal segment longer than the 

 fourth, almost as long as the fourth and fifth together. 



Length 2-2.5 mm., form elongate-oval, nearly parallel- 

 sided. Dorsal surface black, polished punctate, hairy; 

 elytral punctures subserially arranged on disc, becoming 

 minute and sparse at sides and apically; elytral vestiture 

 dual: of sparse longer, thinner, semierect hairs, and 

 dense recumbent, short, broad hairs, the latter less dense 

 at middle of disc and forming a "whorl" toward sides just 

 before middle. Undersurface rufopiceous, opaque except 

 between prostemal carinae; antennal segments 3 and 4 

 subequal; Coronado, San Diego County, on mud flats 

 covered at high tide; Naples, Los Angeles County, among 



shoots of a beach plant (J. O. Martin) 



crotchi LeConte 1874 



REFERENCES 



CASEY, T. L. 



1889-1890. Coleopterological notices. I. With an appen- 

 dix of the termitophilous Staphylinidae of Panama. 

 Ann. N.Y. Acad. Sci., 5:39-198. 

 1912. Descriptive catalogue of the American Byrrhidae. 

 Memoirs on the Coleoptera, 3:1-69. 

 FALL, H. C. 



1901. List of the Coleoptera of southern California, 

 with notes on habits and distribution and descriptions 

 of new species. Occ. Pap. Calif. Acad. Sci., 8:1-282. 

 HINTON, H. E. 



1939. An inquiry into the natural classification of the 

 Dryopoidea, based partly on a study of their internal 

 anatomy (Col.). Trans. Roy. Ent. Soc. London, 89: 

 133-184, 105 text figs., 1 pi. 



