326 Natural History Bulletin. 



other hand there is little differentiation inter se. Studied from 

 specimens taken at Albuquerque, New Mexico. 



ACILIUS. 



Anterior tarsi of male dilated, basal joint with three large 

 palettes and patch of very small ones. Fringing hairs usually 

 long. Intermediate tarsi little or not at all dilated. 



A. FAsciATUS De G. Plate VIII, Fig. 8. 



Basal joint of anterior tarsus much larger in proportion to 

 the others than in any other species thus far studied. The 

 sexual hairs are also very differently arranged, as follows: 

 Basal joint with a very large palette near the proximal angle, 

 two smaller palettes just beyond this, and a patch of very 

 small long-stalked ones crowded together in the other angle. 

 The second and third joints of the tarsus bear only the small- 

 est size of palettes, a median space equal to somewhat less 

 than one-third of the width of the joint being quite bare. The 

 fringing hairs are very long and beautiful, reaching their 

 greatest length in the vicinity of the large palette and becom- 

 ing shorter and stouter as they approach the articulation of 

 the fourth joint. 



The differentiation of the palettes into three sets is very 

 interesting and is the most characteristic feature of this foot. 

 Prof. Nutting to wiiom I showed the drawings and notes has 

 suggested that this indicates a high degree of specialization, 

 the development of three sets differing widely among them- 

 selves, more than offsetting the great reduction in number of 

 palettes with little difference inter se as shown in Thermonec- 

 tes ornaticoUis. One of the species of Acilius {^A. mediatus 

 Say) seems to show that quite possibly these two very dif- 

 ferently appearing feet may be elaborations of a common 

 type — that in the more typical species of Thermonectes the 

 tendency has been along the line of reduction in number of 

 the palettes with maintenance of comparative equality in size 

 while in Acilius the three large palettes seem rather to have 



