57. Front tarsus with 2nd segment nearly 1/4 longer than 

 1st 58 



— Front tarsus with 2nd segment as long as, or shorter 

 than 1st 59 



58. Genital lamellae scarcely twice as long as wide; 

 northern and central California . . tenuipes Aldrich 1894 



— Genital lamellae 4 times as long as wide 



superbus Van Duzee 1921 (part) 



59. First and 2nd segments of front tarsus of nearly equal 

 length canaliculatus Thomson 1868 (part) 



— Second segment of front tarsus distinctly shorter than 

 1st 60 



60. Genital lamellae with a deep incision on upper edge; 

 Santa Clara and San Diego counties 



duplicatus Aldrich 1893 



— Genital lamellae without an incision, normal 61 



61. Wing with a small lobe at tip of 6th vein; costa not 

 enlarged at tip of 1st vein; middle basitarsus with a 

 large bristle above; hind basitarsus only a little yellow 

 at base completus Van Duzee 1921 (part) 



— Wing without a lobe at tip of 6th vein; costa with a 

 long tapering enlargement at tip of 1st vein; middle 

 basitarsus without a bristle; hind basitarsus yellow, 



narrowly black at tip; Humboldt County 



occidentalis Aldrich 1893 



Genus Tachytrechus Walker 



This genus was named for the habit the adults have, 

 of running on the sand or mud, or flying low along 

 the margins of lakes or the seashore. The only ac- 

 count of the immature stages is Lundbeck's (1912) 

 description of the pupa of the European T. insignis 

 (Stannius) which was taken from the sand on a lake 

 margin. The following key is adapted from one by 

 Harmston and Knowlton (1940) for the Nearctic species. 



Key to Males of the California Species of Tachytrechus 



l.Antennal arista normal, pointed, without terminal 

 lamella 6 



— Arista long, with a terminal lamella 2 



2. Femora entirely yellow; central and southern California 

 auratus (Aldrich) 1896 



— Femora yellow with black markings or entirely black 

 3 



3. Front femur broad at base, usually with black marking 

 on outer surface 4 



— Front femur not broadened at base, entirely yellow 

 5 



4. Front femur with a large jet black spot covering nearly 

 the whole of outer surface; lamella of arista scarcely 

 whitish at base; Monterey, Mono, and Inyo counties 

 olympiae (Aldrich) 1896 



— Front femur scarcely infuscated * on outer surface; 

 lamella of arista large with apical 1/2 black, basal 

 1/2 white except for slight narrow infuscation near the 

 stem; Lake Tahoe 



tahoensis Harmston and Knowlton 1940 



5. Hind femur black at base below; bristles on anterior 

 surface of fore tibia longer than the row of bristles 

 on outer posterior surface, the latter row of bristles 

 of decreasing length, those at base much longer than 

 those near distal end; Humboldt County and Sierra 

 Nevada sanus Osten Sacken 1877 



— Hind femur slightly or not at all blackened at base 

 below; bristles of anterior surface of fore tibia not 



453 

 Wirth and Stone: Diptera 



longer than the row of bristles on outer, posterior sur- 

 face, the latter row of bristles of nearly equal length 

 throughout; Tulare County. . spinitarsis Van Duzefl 1924 

 6. Legs wholly black; hind tibia with 2 flattened hr. 



on posterior side near middle; California 



angustipennis Loew 1861 



— All femora blackish-green except for apical 4th; tilii/u- 

 yellow; middle tarsus with 2nd joint flattened; central 

 and southern California granditarsus Greene 1922 



Subfamily H YD ROPHOR IN AE 



Genus Hydrophorus Falldn 



(Fig. U-A9h-j, r-u) 



Flies of the genus Hydrophorus are characteristic 

 skaters over ponds and near the shores of lakes and 

 marine estuaries. The adults (fig. 14:49A) are char- 

 acterized by dull pruinose bodies, long legs with the 

 fore ones raptorial, and long wings with the discal 

 cell especially lengthened. According to Williams 

 (1939) who published a remarkably detailed account 

 of the biology of the Hawaiian H. pacificus Van 

 Duzee, the adults are fond of bloodworms, the larvae 

 of Tendipedidae, which they pull from the mud of wet 

 shores. The immature stages of H. ayalma Wheeler 

 (fig. 14:49r-u;) have been nicely figured by Greene 

 (1923) from specimens collected on the shores of 

 Lake Winnipeg, Manitoba. The following key is adapted 

 from one to the Nearctic Hydrophorus by Van Duzee 

 (1926). 



Key to Adults of the California Species of Hydrophorus 



1. Knobs of halteres wholly yellow 2 



— Knobs of halteres infuscated, at least on outer surface 

 12 



2. Postvertical bristles in a row of 4 or more on each side 



3 



— Postverticals only 2, as usual 5 



3. Scutellum with 2 or more pairs of marginal bristles 



4 



— Scutellum with only 1 pair of marginal bristles; Cali- 

 fornia gratiosus Aldrich 1911 



4. Wing with distinct whitish spots or clouds in the cells 

 and at base; Lake County plumbeus Aldrich 1911 



— Wing without whitish spots, grayish hyaline as usual; 

 Alameda and San Diego counties 



argentatus Van Duzee 1918 



5. Black propleural bristles above fore coxa absent 

 6 



— With 1 black propleural bristle above each fore coxa 

 .. ., 7 



6. Dorsocentrals minute, white; fore femur of male with 

 a deep notch near the tip, its tibia bent; San Bernardino 

 County canescens Wheeler 1896 



— Dorsocentrals black; San Bernardino County 



flavipennis Van Duzee 1926 



7. Face opaque with pollen, the ground color not showing 

 through 8 



— Face showing more or less metallic color through the 

 pollen 9 



.8. Face ochre-yellow; wings with very conspicuous spots 

 on the cross vein and last section of 4th vein; veins 



blackish, scarcely paler at base; Tioga Pass 



alter Parent 1934 



