540 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



subdivisions, however, are never detached phites, but are simply parts 

 of the episterna equivalent to the superior subdivisions (102, 105, 

 109, epm)oi the mesothoracic epimera(^p7?i), and to the subdivisions 

 (111-121, ej)7n) of the metathoracic epimera. The writer formerly 

 (1908) Avrongly identified this last plate with the postparapterum, 

 a sclerite which is absent in the Coleoptera. 



An important sclerite in the pleurum of insects and undoubtedly a 

 primitive plate in the thorax is the trochantin (Tn). This is a plate 

 lying in front of the coxa (text fig. 3, Tn), connected above with the 

 lower edge of the episternum {EjJs) and articulating below by a small 

 condyle (TnC) with the ventral rim of the coxa. Hence, when the 

 trochantin is present, the coxa turns on a hinge line between the coxal 

 condyle of the pluerum (CxP) and the coxal condyle of the trochantin 

 {TnC). The trochantin is well shown in the Mantidre (26, 27, 28) 

 and in the Blattidse (29, 32, 35). In the latter family it is divided 

 into two parts {Tn and tn). The smaller part {tn) is Mhat Comstock 

 and Kochi (1902) call the "second antecoxal piece," but this part 

 carries the coxal articulation and is, therefore, certainly the principal 

 ])art of the trochantin. 



The trochantin is well developed in the Locustidre (43) and the 

 Gr3dlida^ (4G, 47). It is small or rudimentary in the Acridiida? (51, 

 56). In the Plecoptera its upper end is fused with the episternum 

 in the meso- and metathorax (78, 79). In the prothorax it inserts 

 itself entirely between the episternum and epimerum and the coxa 

 (72, 73, Tn), thus separating the latter from its true pleural coxal 

 process. By Avay of reparation to the coxa, however, the trochantin 

 develops a dorsal coxal condyle (72, 73, 74, Tn CxP) in addition to 

 its usual ventral coxal condyle {TnC). It even goes further and 

 actually presents an internal trochantinal ridge (74, TnR) simulating 

 the true pleural ridge (74, PR). This is, of course, a highly special- 

 ized condition. 



The trochantin occurs in typical form in the Euplexoptera (91, 94, 

 98, 100). It is present in 'the prothorax of Bcnacits (Hemiptera) 

 though concealed by the overlapping pleurum (83 Tn). In most of 

 the Coleopterii it is a very small plate in the pro- and mesothorax (99, 

 104, Tn) concealed at the u])per end of the coxa within the coxal 

 cavity. In the SilphidiT (106) and Buprestida' (109), however, it 

 is an exposed plate {Tn) occupying the normal position between the 

 episternum {E ps) and the coxa {Cx). It is absent in the Coleop- 

 teran metathorax. In the Neuroptera (1-17) and Trichoptera (146, 

 148) it is a large plate. In the Lepidoptera (149, 153, 154, 158, 159) 

 it is partially or entirely fused with the episternum, and is not very 

 distinct from an arm of the sternum {S) in front of it. Its ventral 

 coxal articulation is weak or absent. In the Ilymenoptera and Dip- 

 tera the trochantin is either absent or is indistinguishably consoli- 

 dated with the sternum. 



