12 PROCEEDESrGS OF THE NATIONAL MUSEUM vol. 121 



similar to those found in the larvae of Xylomyinae and Beridinae. 

 In addition, pachygastrine larvae are found under the bark of trees 

 as are larvae of Xylomyinae. During the course of time, however, 

 the chaetotaxy and size of the larvae have evolved. 



On the basis of similarity of mouthparts, the Clitellariinae and 

 the Pachygastrinae appear to have arisen from a beridine stock. 

 The former represents a radiation into a new ecological zone, and 

 the latter represents evolutionary improvement for living in an 

 already occupied niche. Clitellariine larvae have mouthparts much 

 the same as beridine larvae except for the labium, which has become 

 more sclerotized and spatulate in the former. This change in the 

 labium is probably an adaptation for feeding on the pulpy flesh of 

 succulents. 



The Sarginae appear to have arisen from a clitellariine stock, 

 probably closely related to the tribe Hermetiini. The mouthparts of 

 the latter are very similar to those of the Sarginae and both groups 

 live in the same type of enAoroment— decaying organic material. 

 Both groups are highly evolved: the mouthparts have degenerated 

 so that the mandibular-maxillary complex is almost indistinguishable. 



The subfamily Nemotelinae, although similar in general appear- 

 ance to the Stratiomyinae, apparently has evolved from a clitel- 

 lariine stock. This cleavage, however, must have occurred shortly 

 after the Clittellariinae had broken away from the pachygastrine 

 stem since all three taxa are closely related (fig. 2). Both adult and 

 larval characters of the Nemotelinae appear to substantiate the con- 

 clusion that the Stratiomyinae and Nemotelinae are not closely re- 

 lated and probably never have been. 



The Stratiomyinae have few characters in common with any of 

 the extant subfamilies. Larval characters indicate that the sub- 

 family probably evolved from a beridine stock at a very early period. 



Because the Chiromyzinae are represented in North America by 

 only Altermetoponia rubriceps — an introduced species — ^no further 

 consideration need be given to the phylogeny of this subfamily. 



Classification 



The classification of the Stratiomyidae presented here is based 

 upon opinions and conclusions drawn from the relationships of the 

 subfamilies presented in the previous section. This system differs 

 somewhat from the classification of James (pers. comm.), which is 

 based upon adult characters. A comparison of the 2 systems is 

 as follows (asterisks indicate genera not seen in immature stages and 

 thus not in my classification): 



