XVIII BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



tioiis. The following are the characters used by Kowarz, * an able Eu- 

 ropean (lipterologist, to define the generic subdivisions: 



1.— Third antt-nnal .joint slender and long 2 



Third joint short and hroad 3 



2._Tho auxiliary vein terminates before the anterior cross- vein Pipizella Eond. 



The auxiliary vein terminates beyond the anterior cross- vein Heringia Rond. 



3.— Frontal triangle of the male comi)aratively large and arched; front of female 



without a tuft of white hairs near the orbit 4 



Frontal triangle not large, of usual form ; front of female with a tuft of white 



hairs near the orbit Pipiza Fallen. 



4.— Hind coxai of male with spinous process; front of female with a distinct trans- 

 verse groove near the middle Cnemodon Egger. 



Male coxje without spinous process; front of female without transverse 

 groove PEXiUMPhil. 



An examination of these characters seriatim will, I think, show their 

 invalidity as generic distinctions. I by no means wish to say that they 

 are without value, or that the names should be abandoned, but that 

 their present substitution is not justified. 



1. All intermediate stages will occur between a long, slender antenna 

 and a short broad one, where it will be impossible to refer a species to 

 either of these divisions without we take an artificial standard. 



2. The same may be said of the termination of the auxiliary vein. 

 What will we do with the species where the termination is opposite the 

 cross vein ? 



3. The presence of a swollen frontal triangle is a useful character, 

 but the same objection may be urged against it as against the two pre- 

 ceding ones. The same feature occurs in species of both Chilosia and 

 Chnjsof/aster, and was formerly made use of, in the former at least. Its 

 acceptance here will, pari passu, necessitate its employment in allied 

 genera. 



4. The presence of a coxal spine is perhaps of greater value, yet we 

 must not forget that the same character is disregarded elsewhere in the 

 family. No one will think of generically separating Xylota bicolor and 

 X. tibialis, or Helophilus distinctus, that has been confounded with H. 

 chrysostomus, on this character. 



The introduction of such fine distinctions is undesirable in any genus 

 when characters of the same or similar nature are unrecognized in 

 allied genera. It is true that arbitrary distinctions in the comparative 

 shape of the antennai, etc., we are compelled to use to a great extent in 

 the Aluscida; cali/ptratw ; but at the same time we must admit the 

 almost insuperable difficulties which these families present to sys- 

 teiiiiitic study; so great, indeed, that there are but three or four ento- 

 mologists (among whom we must award to Mr. Kowarz the first rank) 

 who are capable of interpreting them. 



Two species of Trighjplms have been described byLoew; both of 

 them I have placed under Pipiza, as from an examination of the types 

 * Wieu Ent. Zeitung, iv, 241. 



