No. 1774. TUORAX OF HYMEN0PTERA—8N0DGBA8S. 53 



3. MORPHOLOGY OF THE POSTNOTAL PLATES (POSTSCUTELLA) AND 



THE PHRAGMAS. 



Almost all writers have recognized under some name the postnotal 

 sclerites of the thoracic terga. The nomenclature current amongst 

 Hymenopteran systematists, however, attaches the name "postscu- 

 tellum" to the plate on the surface of the dorsum immediately follow- 

 ing the mesoscutellum (pi. 14, fig. 63, N^), but which, in this order, is 

 the metanotum, since it carries the hind wings. This mistake has 

 arisen from the fact that the earlier students of these insects were 

 Ignorant of the fact that the true postscutellum (the postnotum) of 

 the mesothorax is deeply invaginated and entirely concealed within 

 the body between the mesothorax and the metathorax. A further 

 consequence of this error is the application of the name "metathorax" 

 to the propodeum or first abdominal segment (IT) of the thoracic 

 mass, in spite of the fact that it has no connection whatever with the 

 hind wings. The incorrectness of such a nomenclature is at once 

 apparent when it is seen that it assigns both pairs of wings to the 

 mesothorax. 



The usual interpretations of the back sclerites in the Diptera have 

 been more correct because there is present a large and unmistakable 

 postnotal plate in the mesothorax (fig. 4, PN) distinct from the wing- 

 bearing metanotum. Lowne (1892) calls this the "postscutellum" 

 in the blow-fly. Crampton (1909) distinguishes its three subdivisions 

 in the Tipulidse as the " mediophragmite " and the "pleurophrag- 

 mites." Berlese (1906), however, confuses it with the metathorax 

 in both Tipula and Callvphora. 



Various names have been given by different authors to this post- 

 notal plate. Chabrier (1820) called it the "cloison costale." Strauss- 

 Durckheim (1828) called that of the metathorax in Melolontha the 

 "tergum." Amans (1885) included both the postnotum and the 

 attached phragma under the name of "subpostdorsum." Kolbe 

 (1889) applied the term "phragma" to both the postnotum and its 

 phragma. Audouin (1824) first used the term "postscutellum" in 

 describing the tergum of Dytiscus, but he did not correctly distinguish 

 the parts anatomically, as the present writer has elsewhere shown 

 (1909), yet, the term postscutellum, may very appropriately be given 

 to the tergal plate following the scutellum when the latter is present. 

 However, as will be shown later, the postscutellum in this sense is not 

 one of the subdivisions of the notum, corresponding with the pre- 

 scutum, scutum, and scutellum, but is a separate plate developed inde- 

 pendently back of the true notum. Therefore, the writer formerly 

 (1909) adopted the term "pseudonotum," used by Verhoeff (1903) in 

 the Euplexoptera (Dermaptera), as a general term, but suggested as 

 an alternative the name postnotum. Since, however, Verhoeff did not 



