DIAGNOSIS: This species resembles Optioservus trivittatus (Fig. 81) in 

 appearance but is larger and has very different markings. 



DESCRIPTION: Holotype male: Length 2.3 mm, width 1.2 mm; head and 



thorax shiny black, scutellum ochreous; elytra fuscous brown with 

 yellow-orange markings; venter fuscous brown; entire body covered 

 with short depressed hairs which are much more abundant on ventral 

 surface . 



Head : Black; maxillary palpi four- segmented; antennae testaceous, 

 eleven- segmented, length 0.5 mm, segment eleven twice as long as 

 nine or ten, segment three four-fifths as long as eleven, segments 

 one and two almost as wide as long. 



Pronotum : Length 0.6 mm, width 0.8 mm; sides arcuately convergent 

 anteriorly, disc covered with very shallow punctuations, basal sub- 

 lateral carinae 0.2 mm long extending anteriorly. 



Elytra : (Fig. 83) Wider than thorax, widest near middle; length 1.7 

 mm, width 1.2 mm; strial punctures shallow, separated by distance 

 greater than their width; humeral spot reaching seventh stria and 

 extending to suture, then posteriorly two-thirds of way along 

 elytron; second elongate spot extending from just below middle 

 almost to apex of elytron. 



Venter : Covered with heavy hydrofuge pubescence, especially on ab- 

 domen. Legs ochreous yellow throughout entire length. 



DISTRIBUTION: Missouri 



SPECIMENS EXAMINED: Holotype (male), four paratypes from Roaring River 

 State Park, Missouri, and ten paratypes from Big Spring State Park, 

 Missouri, taken June 1954, July 1954 and December 1968. 



Optioservus pecosensis (Fall, 1907). In clear, cool or cold, gravelly 

 or rocky streams from New Mexico to California and north to Wyoming 

 and Washington (according to Collier) . (May well be confused with 

 0. divergens . ) 



Optioservus quadrimaculatus (Horn, 1870). In gravelly or rocky riffles 

 from Colorado west to California and North to Montana and British 

 Columbia. 



Optioservus sandevsoni Collier, n. sp. {see page 13) (Fig. 82) 



Type locality: Washington Co., Arkansas, 16 June 1962; Lot No. 193. 



Location of type: Holotype, male, and three paratypes, will be deposited 

 in Illinois Natural History Survey Collection. 



DIAGNOSIS: This species resembles Optioservus trivittatus (Fig. 81) and 

 Optioservus ozarkensis (Fig. 83), but may be separated from all 

 other Optioservus by the two spots and one sutural vitta on each 

 elytron (Fig. 82). This type of marking has not been found on any 

 other Optioservus. 



DESCRIPTION: Holotype male: Length 2.6 mm, width 1.3 mm; head and 



thorax black with yellowish-grey pubescence; scutellum yellowish- 

 orange; elytron dark red-brown with yellowish-orange spots and 

 sutural vitta, striae not deeply punctured on elytron. 

 Head : Black; clypeus covered with greyish pubescence; maxillary 



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