ILLINOIS BIOWGICAL MOXOGRAPIIS [40 



SOME PHYLOGENETIC CONSIDERATIONS 



With the hypothetical type of coleopterous head in mind, it is possible 

 to note the lines of development that have taken place within the various 

 groups. Structures have developed away from the primitive condition 

 with varying degrees of rapidity, and sometimes in different directions. 

 It is difficult from this study to decide on the amount of importance to 

 attach to the change that may take place in a particular structure, and to 

 average the degree of primitiveness as a whole of the development of the 

 structures characteristic of a group, and to indicate with precision the 

 place in the primitive scale of each group. As previously mentioned, owing 

 to the wide field covered in this investigation it was impossible to find 

 time to study a large representation of genera within each family. Such 

 a study should help one considerably in reaching clearer conclusions as to 

 the arrangement of the genera in the primitive scale. Using this study 

 as a basis, it is quite possible, however, to discuss the relative importance 

 of the structural changes e.xhibited by the different groups, and to suggest 

 possible inconsistencies in the present arrangement of certain genera. 

 Statements made in the following discussion are based only on this study. 



The characteristic possession by the .'\dephaga (Figs. 2-10, 23-24, 

 150-158, 297-305, 444-452) of the occipital suture, of complete epicranial 

 arms, of a generalized position of the antennariae and of the pretentorinae, 

 of a generalized form of labrum, and of tentorium, would force such families 

 as the Cicindelidae, Carabidae, Amphizoidae and Omophronidae into a 

 primitive place in the phylogenetic scale, in spite of their specialized ventral 

 surface. No other large group shows as many primitive characters. The 

 genera of the above mentioned families show a great similarity in all their 

 structures and must be closely related. Of these families Omophronidae 

 possibly possesses the most generalized dorsal surface, though the occipital 

 suture in Omophron is not nearly complete, and does not show on this 

 surface. Omophron can hardly hold an intermediate position between 

 the Carabidae and the Haliplidae, for the latter family, as represented by 

 Peltodytes, shows little similarity with any other family of the .\dephaga. 

 The form of the head is distinctly specialized, being globular, with enor- 

 mous eyes, and the mouth-parts and the very small labrum are directed 

 distinctly ventrad. The occipital suture is probably lacking, the epicranial 

 suture is shorter than in any other genus of the .\dephaga. On the ven- 

 tral surface, the metatentorinae extend only half-way between the oc- 



