8 R. W. CROSSKEY 



clearly close relatives may assume widely differing and sometimes bizarre shapes, 

 and the gill form cannot normally be used as a major differential character between 

 genus-group segregates. The form of the terminal abdominal hooks or tubercles and 

 the form and degree of sclerotization of the abdominal cuticle provide some useful 

 characters ; and the presence or absence of transverse rows of backwardly-directed 

 irregular spiny processes situated anterodorsally on the dorsum of the last few 

 abdominal segments is often of major taxonomic importance (for brevity and 

 simplicity these have been termed spine-combs throughout the text : see Text-fig. 

 168). In addition to the spine-combs (if present) the pupal abdomen has a rather 

 constant arrangement of main hooks on the dorsum and venter for which the term 

 onchotaxy is here used : in general the onchotaxy has a fixed basic plan in each genus 

 which may or may not be supplemented by supernumerary small fine hooklets or 

 variously modified setae, the form and arrangement of which may be of taxonomic 

 value. Some island and phoretic forms show extraordinary aberrant departures 

 from the normal basic onchotaxy. 



Cocoon characters. The discreteness of form, modifications of shape and closeness 

 of weave (for instance, presence or absence of fenestration) of the cocoon provide 

 important taxonomic characters which can be of use at species-group or superior 

 level. In some primitive forms the cocoon material forms almost a communal 

 matrix, but most often each pupa is invested individually in its own discrete cocoon 

 with definite shape : this is termed slipper-shaped if the cocoon is simple and lacks a 

 neck or collar connecting the two slides anteriorly (Text-figs. 164 & 166) and shoe- 

 shaped if the two sides of the cocoon are connected anteriorly by a raised neck or 

 collar (Text -figs. 165 & 167). Reduction of the cocoon to cover only the pupal 

 abdomen or to a mere few threads and a holdfast may occur, and provide a taxon- 

 omic feature for rare groups ; likewise, incorporation of inorganic matter in the 

 texture of the cocoon is associated with some taxa and not others. The presence of 

 a simple or divided anterodorsal median projection from the body of the cocoon is 

 sometimes a species-group character. 



Larval characters. The morphology of the Simuliid larva and a detailed discussion 

 of the characters of taxonomic value was given in my earlier paper on the larvae of 

 Ethiopian black-flies (Crosskey, i960). The terms used for larval characters are the 

 same as in the previous work and are shown on the accompanying Text-figs. 7-15. 

 The head pattern is described as negative when the spots themselves are pale with 

 dark infuscation around them (Text-figs. 232-234), and as positive when the spots 

 are dark (Text-figs. 235-240). The larval body shape and the cuticular ornamenta- 

 tion of variously modified setae (when present) provide useful characters at species- 

 group or genus-group level. In the hypostomium the rows of hypostomial setae 

 may either lie subparallel to the sides of the hypostomium (as Text-fig. 303) or they 

 may diverge from the hypostomial margins posteriorly (as Text-fig. 304) and this 

 character tends to divide certain groups of genus-group taxa from others. Particular 

 attention should be drawn to the comb-teeth of the mandible (Text-fig. 13) : these are 

 three in number and lie immediately basad of the main apical tooth ; their size 

 relative to each other and their degree of differentiation from the apical teeth or from 



