1898.] NATURAL SCIENCES OF PHILADELPHIA. 169 



In English we have but one word " cheek " for the two German 

 words Wange aud Backe. The Wange is dorsad of the Backe, In 

 Latin the word " gena " refers rather to the upper part of the cheek, 

 the word " bucca " to the lower part. For these reasons and be- 

 cause the words bucca and Backe are so nearly alike, it has seemed 

 to me wise to translate Wange by gena and Backe by bucca. The 

 bucca is sometimes clearly defined, cephalad, from the vibrissal 

 ridge by a distinct steep edge (I have never been able to see a 

 suture here), at other times it is not so defined and the line of sepa- 

 ration is an imaginary one, more or less clearly indicated by dif- 

 ferences in the characters of the hairs and bristles of the bucca and 

 the vibrissal ridge. That portion of the bucca which is on the occi- 

 pital surface is bounded by distinct sutures. The whole bucca is 

 hairy or bristly, the hairs and bristles varying in number and size 

 in different species. 



Mesad of the arms of the frontal suture, constituting the lateral 

 boundaries of the facial fossa, are two distinct ridges, one on each 

 side of the face. These are the vibrissal ridges, so-called because on 

 them the stout bristles called vibrissae are inserted. They were 

 called the faeialia by Desvoidy, by Walker and by Baron Osten- 

 Sacken, but the term used by Professor Brauer, " Vibrissenleisten," 

 meaning vibrissal ridges, is so much more appropriate, that I prefer 

 to sacrifice priority to good sense. If we follow the vibrissal ridge 

 dorsad we find that it diminishes in width and gradually disappear^ 

 from view under the gena. If we follow it ventrad we find that it 

 gradually increases in width, being largest at a point called the 

 vibrissal angle, where the largest of the vibrissa? is inserted. The 

 position of the vibrissal angle with relation to the edge of the mouth- 

 opening is not the same in all genera, being sometimes very close to 

 it and sometimes rather remote. In all the genera to be considered 

 in this paper, however, except Pollenia and Paracompsomyia, the 

 two are very close together. Dorsad of the vibrissal angle we 

 usually find one or more vibrissa? which are much smaller than the 

 one inserted at the angle. Dorsad of the smaller vibrissa? the ridge 

 is usually more or less thickly beset with minute bristles as far as 

 or beyond the ventral end of the arm of the frontal suture. Ven- 

 trad of the angle there are usually a few vibrissa?. 



The bristles of the legs require also a few words of introduction. 

 These bristles have not as yet received the study that they deserve 

 in the Muscidse. I believe there is a typical arrangement of these 



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