Coleopterological Notices, V. 575 



PLEGADKRUS Erichs. 



This is one of the most peculiar genera of the Histeridse, although 

 there are many singular forms which at first sight appear to be 

 more isolated ; it is generally found however, that the divergence 

 in these cases is less real than apparent, the external organs and 

 appendages of the body merely being specialized in various direc- 

 tions. Here there is a radical difference in the formation of one of 

 the most important of the fundamental segments of the body, prob- 

 ably accompanied by corresponding modification of the internal 

 anatomy. The division of the prothorax into two transverse lobes 

 is met with in some other widely separated groups, such as the 

 Paussidse, but in the present family all forms leading up to or fore- 

 telling this peculiarity have; seemingly disappeared, so that it is 

 scarcely possible to reason upon its true etiological significance.^ 



The deep diverging fossae of the prosternum are obviousl}^ an ex- 

 treme development of the usual prosternal striae, but the transverse 

 excavation uniting them is, as far as known to me, without any 

 suggestion of parallelism in the entire family. I dwell with some 

 emphasis upon this character because it has never been given the 

 weight which apparently belongs to it. The genus should in fact 

 be separated rather widely from those with which it is now^ asso- 

 ciated. 



The species are moderately numerous in the United States, and 

 may be distinguished by the following table : — 



Anterior prosternal lobe longer than wide, more or less acutely rounded 

 behind, and strongly and rather closely punctate ; punctures of the 

 elytra rounded and not longitudinally confluent ; transverse pronotal 

 sulcus always deep and conspicuous. 

 Punctures of the elytra not very dense, distinctly separated ; apical lobe 

 of the pronotum much shorter than the basal. 

 Margin of the pronotum broad, less convex. 



Meso-metasternal plate densely, coarsely punctate sayi Mars. 



Meso-metasternal plate more finely and sparsely punctate. 



consors Horn. 



Margin of the pronotum narrower and more convex ; entire body narrower 



and less depressed, piceous-brown, polished, sparsely and coarsely 



sculptured fraternus Horn. 



1 The transverse row of prosternal fovese in Griymma does not bear much 

 resemblance to the division in Plegaderus, for there is no sign of a division 

 upon the dorsal surface. Griymma should probably be referred to the Histrini, 

 the fovese being the delimiting line of the prosternal lobe. 



