PART I. 



The External Anatomy of Tachytes distinctus. 



Inasmuch as the external anatomy of each genus of the 

 North American Larridae could not be examined, the writer 

 has selected a large and common species, Tachytes distinctus, 

 a typical example of the family, as the basis for the short 

 study herewith presented. 



The female of this insect is fully twice as large as our 

 common honey-bee (Apis mellifica), of stout build, though 

 rather elongate, and in general of a dull black color, partly 

 concealed by pubescence. The yellowish wings are smoky 

 apically; the legs spinose, and largely of a ferruginous color. 

 The male is smaller, and usually more slender than the female. 

 A specific description of the insect will be found in the sys- 

 tematic portion of this paper, while notes on its habits are 

 given on pages 194-197 (96-101) of the biologic section. 



In order to bring to light more clearly the often none-too- 

 well defined areas and sclerites, the pubescence and pile should 

 be removed from the head and thorax of the insect. 



Head. 



(PI. XXII, fig. 6, front view.) 

 Areas and Sclerites. 



The head of this type of insect does not present the com- 

 paratively generalized condition to be found in the cockroach, 

 for example, where some of the sclerites are definitely bounded 

 by sutures. On the other hand, they have very largely dis- 

 appeared by fusion with one another. 



Compound Eyes. The large, greenish compound eyes con- 

 verge towards the upper portion (vertex) of the head, with 

 the effect of making the interocular space at that point only 

 about one-half as wide as the space between the eyes at the 

 base of the mandibles, to which they nearly extend. This 

 interocular space at the vertex varies in different species, and 

 is for that reason of considerable taxonomic value. 



(125) 



