100 ENTOMOLOGICAL NEWS. [March, '09 



subpostdorsum (including the phragma) of Amans (1885), 

 the metaphragma (including the pseudonotum and true phrag- 

 ma) of Kolbe (1889), and the acrotergite of the following 

 segment, in most cases, of Berlese (1906). 



The metanotum of Dytiscus is a complicated plate and is sub- 

 divided by distinct lines into six regions (figs, i, i, 2, 2, 3, 3, 

 4). Two of the subsclerites (i and 4) form the anterior and 

 posterior regions of the notum respectively. Each is widened 

 mesially. The former sends posteriorly two arms which inter- 

 lock with an anterior median tongue of the latter forming the 

 floor of the median notal groove (G). The other subsclerites 

 (2, 2, 3, 3), as will be seen from the drawing, are paired and 

 together occupy the greater part of the notum. 



An examination of the ventral surface of the tergum (fig. 

 2) reveals the fact that all of the lines appearing on the sur- 

 face of the notum, except those defining the anterior subscler- 

 ite are simply the external marks of internal ridges (iv and B}. 

 In addition to these are the anterior and posterior marginal 

 ridges of the notum (ANR and PNR}. The ridge w is peculiar 

 to the Coleoptera, the other three are common to nearly all 

 insects. 



Hence, it must certainly be evident to anyone who will ver- 

 ify these drawings by a study of any species of Dytiscus that 

 four transverse tergal plates do not actually exist, and that only 

 the imagination of a person intent upon establishing such a 

 generalization could make any such construction out of the 

 facts. 



If, now, we examine Audouin's drawings (figs. 3, 4) of the 

 metatergum of Dytiscus circumnexus, we are forced to admit 

 that he made separations where he wanted them regardless of 

 the true anatomical structure and combined other parts that 

 are in nature distinct. Figures 3 and 4 are enlarged copies of 

 Audouin's drawings. His first division, the prescutum (psc), is 

 correct in a general way. The second, the scutum (set), is 

 likewise, disregarding details of shape. Here, it will be seen, 

 Audouin's typical example of the scutum has this plate divided 

 into two halves by a posterior extension of the prescutum. It 

 is when we come to the next division, the scnteUuiu (set), 



