AMERICAN DIPTERA. 147 



scale-like and strongly appressed as in species of Ablautus, or 

 it may, as in Cophura fallei and Stcnopogon jubatus, form 

 an erect crest extending from the pronotum to the scutellum 

 along the middle line. The pleura, in the more bristly species, 

 is nearly destitute of pile and bristles; however, bristles or 

 hair, or both, are found usually upon the hypopleura, and fre- 

 quently varying amounts of pile, never bristles, upon the 

 meso- and sternopleura. The scutellum may be wholly bare, 

 with bristles on the posterior margin, wholly pilose, or with 

 both pile and bristles. The ground color of the thorax, as 

 is often that of the abdomen, is more or less obscured by the 

 presence of a bloom which plays an important part in de- 

 scriptive work. 



Abdomen. — The abdomen is composed of eight segments 

 and is firmly united to the metathorax by its full width; it 

 presents many variations in form, being usually long and 

 slender (Deromyia and Microstylum) , sometimes much shorter 

 and broader {Pycnopogon and Laphystid) , in most cases slightly 

 tapering toward the tip, but in the male of Nicocles distinctly 

 expanding from the base of the third segment to the tip of 

 the fifth, and distinctly flattened dorso-ventrally distally. 

 The eight segments are easily discernible in most cases; the 

 seventh and eighth in the male Nicocles not apparent from 

 above, but from the side are seen partially retracted within 

 the sixth ; in Laphystia and Psilocurus the terminal segments 

 are apt to be retracted and are seen with difficulty. The sec- 

 ond segment, near its base, bears a distinct groove bordered 

 by two rows of punctate spots which at first glance appear to 

 divide the segment. The male hypopygium is of little value 

 at present in the separation of genera; in most genera the 

 several parts are closely applied to each other, but in Cera- 

 turgus, Ceraturgopsis and Sphageus, they do not meet, but are 

 so separated as to give the end of the abdomen a " broken-off " 

 appearance. The female ovipositor is usually armed with a 

 terminal circlet of spines ; in Laphystia, Tricles and Psilocurus 

 these are not apparent. The abdomen is variously clothed 

 with pile and bristles; the pile may be microscopic, leaving 

 the surface apparently bare to the unaided eye, or it may be 



TR.\NS. AM. ENT. SOC, XXXV. APRIL, 1909. 



