168 PROCEEDINGS OF THE ACADEMY OF [1898. 



Usually the most caudal pair of lesser ocellar is somewhat larger 

 than the rest, sometimes much larger, and it has received the spe- 

 cial name post-vertical pair. When it is much larger and at the 

 same time is separated by quite a space from the next pair (as in 

 the females of Myospila, Muscina and Graphomyia) the post-verti- 

 cal really seem to be an independent pair of bristles, but when (as 

 in Musca and Morellid) they are hardly distinguishable in size, are 

 as near the next pair as that pair is to the next in the series, and 

 still more when we find similar bristles even caudad of the post- 

 verticals themselves it is clear that they belong to the lesser ocellar 

 series. 



In some species we can see, in the middle of the frontal vitta, a 

 more or less distinctly differentiated dorso-ventral stripe. The ven- 

 tral end of this stripe is not much above the ventral end of the 

 frontal vitta itself. Dorsad it broadens out and then divides into 

 two branches, one of which passes on each side of the ocellar emi- 

 nence to the vertex. Inserted on the vitta some little distance 

 below the anterior ocellus and close to this stripe (over which they 

 decussate) we find in some species a pair of rather small bristles 

 which I call the preocellar. 



Bristles which are inserted on the geno-vertical plate are called 

 orbital. 



On each side of the face at the ventral end of the arm of the 

 frontal suture, begins what is called the transverse impression of the 

 face. This is at first a rather broad shallow depression. It passes 

 almost horizontally laterad (becoming narrower as it proceeds) ven- 

 trad of the eye, and can be readily traced as far as the ventro-cau- 

 dal angle of the eye where it usually seems to end. Sometimes, 

 however, it can be seen to be continuous with a suture of the occi- 

 put which runs from the latero-ventral angle of the great foramen 

 toward and sometimes to the ventro-caudal angle of the eye. 



That part of the side of the face which is dorsad the transverse 

 impression, laterad of the arm of the frontal suture and mesad 

 of the eye is called by the German authors the wange. For this, I 

 suggest the word gena, for reasons which will appear later. The 

 gena is continuous dorsad with the geno-vertical plate. 



Ventrad of the transverse impression and ventrad of the eye, ex- 

 tending ventrad to the edge of the mouth opening, cephalad to the 

 vibrissal ridge, and continuing caudad on the occiput to the great 

 foramen, is the part which the German authors call the Backe. 

 For this I suggest the word bucca. 



