Rowland M. Shelley 



spur or a black dot; in the residual southwestern intergrades, the structures 

 are elevated and often produced, but lack an apical spur or black dot 

 (Shelley 1990a, Figs. 7-11). The strongest, most pronounced coxopleurae 

 are in T. californiensis and T. erythrocephalus (Figs. 13-17, 40-41). 

 In the absence of the caudal legs, this coxopleural feature also distinguishes 

 T. spinicaudus from T. posticus in their areas of sympatry. 



Ultimate legs. The robust, heavily sclerotized, forcipulate caudal 

 legs are the most obvious diagnostic trait of the Plutoniuminae and 

 readily identify Theatops in the United States. Occasionally distended 

 (Figs. 7, 19), the legs typically extend directly caudad basally then 

 curve towards each other and converge such that the tips either meet 

 or cross. They are believed to hold prey for feeding, and this can 

 probably occur either apically, as the sharply pointed tips could puncture 

 most prey organisms, or basally, with the prey being squeezed or pinched 

 by the legs. The caudal legs are more heavily sclerotized than the 

 tergites or the other appendages, but the inner or medial surfaces in 

 many individuals are particularly hard, much more so than the outer 

 surfaces. Perhaps the caudal legs serve to kill prey by crushing or 

 puncturing as well as to hold it. 



The outer surfaces of these legs (dorsal, ventral, and lateral) 

 are usually gently curved to flattened, but the medial surfaces are 

 often strongly flattened, such that there are sharp ventro- and dorsomedial 

 corners that are often elevated above the ventral and dorsal surfaces, 

 forming a ridge. The ridge sometimes points mediad rather than ventrad 

 or dorsad, such that the medial surface is slightly recessed, in some 

 individuals being slightly concave rather than flat. These ridges or 

 corners may be linear or irregularly and lightly scalloped, and are 

 often ornamented with variable teeth or spurs. Ventrally, the number, 

 size, and arrangement of the teeth vary greatly in T. spinicaudus, T. 

 phanus, and the southwestern population of T. posticus (Figs. 19-30, 

 35-38; Shelley 1990a, Figs. 7-11), whereas there is usually a single 

 distal tooth in T. californiensis and T. erythrocephalus (Figs. 13-17, 

 40-41). Dorsally, there is less ornamentation, but occasional individuals 

 show a serrated margin with several fine teeth (Figs. 7-9, 33-34). 

 The distomedial prefemoral spurs in T. spinicaudus and T. phanus 

 are really at the distal corner of this ridge; consequently, the dorsal 

 surfaces of the legs hold taxonomic utility in distinguishing these species 

 from T. posticus, particularly in areas where T. posticus and T. spinicaudus 

 are sympatric. Although differing in the presence (T. posticus) and 

 absence (T. spinicaudus) of the median suture on the ultimate tergite, 

 they are most readily distinguished by the presence or absence of the 

 distomedial prefemoral spur. Variation on the ventral surface holds little 



