12 PROCEEDINGS OF THE ACADEMY OF [Jan.. 



for the prothorax, and it would appear that if such structures ever 



existed in the pronotum they have since been lost through reduction 



or fusion with the scutum and scutellum. 



The Prcescutum. — As has been stated, it is impossible to distinguish 



a prsescutum in the prothorax, but in the mesothorax this sclerite is 



frequently represented by a well developed phragma (fig. 1, Nj). 



This phragma is apparently a portion of the tergum drawn inward and 



downward by muscular tension, and is 



separated from the scutum by the line 



of attachment of the intersegmental 



membrane, beneath which the phragma 



projects into the body cavity. 



In his earlier works Audouin did 



not distinguish between the phragma 



and the triangular portion of the 



scutum immediately behind it (N 23 ), 



Fig-. 1- — Macroxyela. — Dorsal terming both together the prsescutum. 



view of the mesothorax, show- T ,, • i , i r n , t 



ing the subdivisions of the ter- In tms lisa § e he has been followed by 



gumornotum. For reference Packard, '98; but most authors use 



letters, see list at end of the , , , 



paper/ the word prsescutum as synonymous 



with Kleuker's protophragma — in 



other words the prsescutum is only the anterior phragma of the tergal 



region. 



The prsescutum of the metathorax is frequently fused with the 

 postscutellum of the preceding segment or it may be greatly reduced. 

 On this account Kleuker, '83, terms the second phragma the deutero- 

 phragma, whether it is composed of the mesothoracic postscutellum, 

 the metathoracic prsescutum, or of both together. It would seem 

 preferable, however, to use Audouin's terminology, which is not only 

 more exact, but also has the right of priority. 



On either side of the mesothoracic prsescutum of such insects as 

 Myrmeleon, Mantispa, etc., are two bridge-like plates lying just in 

 front of the wings, and connecting the tergum with the upper portion 

 of the episternum. These plates appear to represent the so-called 

 prsesegmental lamellse described by Voss, '04, in the thorax of Gryllus. 

 Since these plates are not internal lamellse, in most insects, but occur 

 usually as external sclerites, they will be here referred to as the prseseg- 

 mental sclerites. 



The Scutum. — The thorax of Dytiscus, which Audouin, '24, chose as 

 his type for insects in general, is too greatly modified to show the nor- 

 mal relations of the tergal subdivisions, but fortunately Audouin, '32, 

 has given a more serviceable description in his translation of MacLeay's 



