42 R. W. CROSSKEY 



4 Cephalic fan with two types of ray, a few very stiff strongly sclerotized blackened 



rays clearly differentiated from fine pale rays on either side (Text-fig. 325). Head 

 with strongly convex sides and cephalic apotome broadest near the middle (Text- 

 fig- 3 2 5)- Hypostomium with group of deeply sunken median teeth flanked by 

 two very prominent groups (Text-fig. 326). Dorsum of cuticle coarsely shag- 

 reened. [St. Helena Island only] . . . DEXOMYIA sgen. n. (p. 49) 



- Cephalic fans normal, rays not clearly differentiated into these two types. Head 



normal, sides not strongly convex and cephalic apotome widest posteriorly. 

 Hypostomium not of this shape. Surface of cuticle more or less smooth . . 5 



5 First five abdominal segments with paired dorsolateral subconical tubercles (Text- 



fig. 230) . Most of thoracic and abdominal cuticle, including the proleg, extensively 

 covered with elongate scale-like setae (Text-figs. 230, 231) ; setae particularly 

 aggregated on abdominal tubercles and making these conspicuous even when 

 smaller than normal. Postgenal cleft exceptionally large and subcircular (Text- 

 fig. 261), occupying most of venter of head capsule 



EDWARDSELLUM Enderlein (p. 101) 



- Abdominal segments without paired dorsolateral swellings, at most slightly pro- 



duced but then without covering of setae. Body cuticle usually without such 

 vestiture, if (albivirgitlatum-group) with conspicuous simple scales these not ex- 

 tending on to proleg. Postgenal cleft usually not of this form .... 6 



6 Cuticle of both thoracic and abdominal dorsum with large flat scales, very easily 



visible. Postgenal cleft elongate subelliptical (Text-fig. 259). Apex of hypo- 

 stomium as in Text-fig. 281, two teeth at each end of the normal row of nine un- 

 usually strong and produced forwards. Outline of body shape as Text-fig. 287 



albivirgulatum-group (ME TOMPHAL US) 



- Cuticle bare or with different vestiture, if abundant setae present on cuticle of both 



thorax and abdomen then minute and hair-like or fan shaped, if large erect scale- 

 like setae present these confined to posterodorsal part of abdomen. Postgenal 

 cleft not of this shape. Hypostomium normal. Body shape as in Text-figs. 224, 

 226, 228 ............. 7 



7 Dorsum of thorax and abdomen with minute inconspicuous erect fan-shaped setae and 



abdomen without ventral papillae. Mandible with one serration only on inner 

 margin, or at most only a trace of second. Head capsule almost totally unpig- 

 mented BYSSODON Enderlein (p. 44) 



- Cuticle either without deeply divided fan-shaped setae, or if these present then 



lying mainly recumbent and abdomen with ventral papillae. Mandible with two 

 or more serrations, inner margin rarely irregularly jagged. Head capsule normally 

 with distinct pigmentation (except sometimes creamy white without obvious 

 marking in bovis-group) .......... 8 



8 Ventral papillae present, subconical (Text-fig. 224), sometimes small and rounded. 



Rows of hypostomial setae lying subparallel to lateral margins of hypostomium 

 (Text-figs. 269-273, 303), median and corner teeth of hypostomium usually 

 strongly prominent (Text-figs. 271-273). Mandible with middle comb-tooth 

 smaller than first or third (Text-fig. 291). Body form usually as in Text-fig. 224. 

 Head pattern usually negative (Text-figs. 232-234). Posterior circlet with 

 fewer hooks (from 60-115 rows of 8-16 hooks). Antennae usually long and 

 slender (Text-fig. 289), longer than stem of cephalic fan ..... 9 



- Ventral papillae absent (Text-figs. 226, 228). Rows of hypostomial setae diverging 



posteriorly from lateral margins of hypostomium (Text-figs. 275-279, 304), 

 median and corner teeth of hypostomium not strongly prominent (Text-figs. 276- 

 280). Mandible with large comb-teeth forming a regularly graded or subequal 

 series (Text-figs. 300-302). Body form as in Text-figs. 226 or 228. Head 

 pattern always positive (Text-figs. 237-240). Posterior circlet with conspicuously 



