HORSE-FLIES AND WESTERN AGRICULTURE, 15 



interiorly, very close to epicranial suture, by a fine dark-brown line. Lateral 

 surface of head capsule with a dark fine line from middle of the main dorsal 

 stripe to the point where tip of cardo attaches. Processes at anterior part of 

 head capsule, and anterior tentorial arm (D), heavily chitinized, dark brown. 

 Dorsally and laterally the head capsule is formed by fusion of the immovable 

 labrum, the clypeus, the epistoma, the membranous bristle-bearing projection 

 partly representing the frons, and the epicranium ; posteriorly the capsule is 

 closed by a convexly rounded wall limiting the occipital foramen behind, and 

 ventrally it is bridged by the large median gular plate, limiting the occipital 

 foramen in front. Occipital foramen ventral, large. All anatomical elements 

 of the cranium are recognized principally by those criteria by which they are 

 characterized throughout the entire insect class, sutures being present only to 

 a very limited extent. Labrum about one-fifth the length of entire head cap- 

 sule, very narrow, compressed, keel shaped, with dorsal surface bent down- 

 ward like the bill of a bird of prey, whitish, membranous, with the inside en- 

 forced by one pair of long splinter-like chitinizations ; posteriorly united with 

 clypeus. Clypeus flat, ovate, almost circular, diameter about one-third the length 

 of labrum'; shiny yellow, with posterior one-third somewhat darker. Epistoma 

 (D) characterized by socket with which mandible articulates dorsally; 

 developed as separate sclerite, forming a strong frame on each side of clypeus ; 

 anteriorly prolonged as a slender process, which projects close to and along 

 the side of posterior half of -labrum; posteriorly flattened into a triangular 

 plate. From the anterior margin of this latter (D ) , the aforementioned articulat- 

 ing socket projects on the inside, reaching forward as far as half the length of 

 the slender process along the labrum ; posteriorly and also on the inside of the 

 epistoma the long, chitinous rodlike anterior tentorial arm attaches, extending 

 posteriorly into the. interior of the cranium, reaching and merging into the 

 lateral border margin! 

 of the occipital fora-f 

 men(iT). Frons not de- 

 veloped as a definite 

 structure. Epicranium 

 occupying main part of 

 entire head capsule, dor- 

 sally divided by the lon- 

 gitudinal median epi- " Fig. 11.— Full-grown larva of Tabanus punctifer* 

 cranial suture. Each 



epicranial half with process containing fossa for ventral mandibular condyle (D ) . 

 Laterally and anteriorly the chitinous margin of the epicranium runs obliquely 

 upward and outward from the base of process for dorsal mandibular articula- 

 tion to the tip of process for ventral mandibular articulation. Articulating 

 basal membranes of antenna and of mandible united with a membranous ele- 

 ment, probably corresponding to angulus frontalis (a well-developed part of 

 frons in many insect larva?, for instance, the beetle larvae), forming together 

 a forward-extending structure very similar to an inflated bag (/). Dorsally this 

 bag is attached to the anterior lateral chitinous margin of the epistoma ; 

 ventrally, along a V-shaped line, to the exterior part of basal margin of 

 mandible ; numerous conspicuous hook-like bristles set distally on the top ; 

 a short, straight, thick chitinous rod present in the ventral wall between the 

 patch of bristles and the ventral articulating condyle of the mandible (B). The 

 tendon of the mandibular exterior (=abductor or extensor) muscle developed 

 from inner end of rod. Hypostomal margin of epicranium rather short, longi- 

 tudinal, and curved, reaching from process for ventral mandibular condyle 

 to the small cusp where the end of the cardo articulates. Gula a comparatively 

 large plate, twice as long as wide, almost as long as labrum, shaped like a 

 coat-of-arms, anteriorly with emargination ; bridging the epicranial halves 

 behind the posterior ends of the cardines. Tentorium represented only by the 

 anterior tentorial arms mentioned and described above ; tentorial bridge or 

 posterior tentorial arms not developed. Optic spot single, dark, placed in the 

 middle of oblique lateral line of epicranium. Antenna distinct, three jointed, 

 with very small distal joint ; long, slender, cylindrical middle joint placed ante- 

 riorly on the brownish, chitinized, somewhat arcuate, very flattened and pos- 

 teriorly extended basal joint. Mandible compressed, vertical, separated into a 

 distal and proximal division. Distal division (described by authors as the en- 

 tire mandible ) strongly chitinized, falciform, movably connected like the blade 

 of a penknife with the proximal division ; proximal division consisting of a 



