386 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Taf. I, Fig. 6, md), retain the palpus, wMcli is represented by a single se- 

 tose bristle, the remnants of the large part of the Xanplian third leg. The 

 teeth on the cutting edge in Branchipus stagnalis are finer and more nu- 

 merous than in the two other families. 



The first maxillce. — Succeeding the mandibles are two pairs of maxillse 

 in the Limnadiadce and Branchipodidce, while in theApodidw there appears 

 to be but a single pair of maxillae, which are succeeded by a rudimen- 

 tary gill-beariug appendage, the maxillipede. The first pair of raaxilloe 

 in Limnadia gif/as are described and figured by Lilljeborg; those of 

 Ustheria mexicana by Claus. According to Lilljeborg the first maxilla 

 of Limnadia consists of but a single lobe with very numerous uniformly 

 dense, fine, slender, and very long setose setse. 



In the ApodidcD the first maxillie consist of two parts, the basal (Plate 

 XXI, figs. 9, 10), which consists of a single large chitinous piece, with 

 the free cutting edge provided with two kinds of teeth, an inner sub- 

 nwirginal row of stout, acutely triangular teeth, while there is a mar- 

 ginal row of hair-like setae. In Lepidurus the external portion of the 

 cutting edge is somewhat differentiated, there being here, as seen in 

 Plate XXI, fig. 0, a specialized portion with three stout teeth ; this 

 becomes obliterated in Apus lucasanus, but in the larva of the same 

 species, as Dr. Gissler's drawing (Plate XXXV, fig. 5) shows, this por- 

 tion is at first separate from the rest of the cutting edge, and in Lepi- 

 dtirns this feature is retained in adult life. Situated close behind the 

 large chitinous portion and loosely connected with it at base is what I 

 should regard as the palpus (Plate XXI, figs. 7, 8, 13); that this should 

 be regarded as a portion of the first maxilla is, I think, proved by ref- 

 erence to the condition of the maxilla in the larva. By reference to Dr. 

 Gissler's figure of the maxilla of the larval Apus lucasamis this palpus- 

 like portion is clearly seen to be a large fiat bilobed portion lying behind 

 but next to the outer part of the cutting edge of the maxilla. 



The maxilla proper, i. e., the cutting or main portion of the appendage, 

 is with good reason homologizcd by Lankester with the first endite or 

 coxal lobe (bis gnatliobase) of the feet of A|)us. The piece which we 

 regard as the palpus, Lankester is apparently disposed to regard as a 

 part of the maxilla, and not, as Zaddach thought, the second maxilla. 



In the Branchipodidce the first maxillae have been best described and 

 figured by Spaugenberg (Taf. I, fig. 5). It consists of a broad, flat 

 maxilla, the inner edge, i. e., that corresponding to the cutting toothed 

 edge of the maxilla of Apus, but which is smooth, with fine, delicate, 

 hair-like setse; while appended to it on the hinder side is a large palpus 

 with long, slender, stiff setie. The same parts are reprcsente< I by Dr. Giss- 

 ler in the first maxilla of the larval Streptocephahis texamis (Phita XXXIV, 

 fig. C), where the maxilla without setse and its stout palpus with two 

 sets of setoe are represented. When the larva is 5 millimetres in length 

 a considerable change has taken place in the palpus ; one of the outer set 

 of bristles has become barbed; while the inner set, originally composed 

 of three setose bristles, is now composed of eleven setae. 



The second, maxillce. — In Limnadia gigas, according to Lilljeborg, the 

 second pair of maxillae are very much smaller than the first pair, and are 

 rounded on the free edge, which is ijrovided with long setiferous bristles 

 and short stout ones. 



In the advanced larva of Ustheria according to Claus's " TJntersuchun- 

 gen," etc, Taf. xix, fig. 1, the second maxilhe are very small, slender, two- 

 jointed appendages, consisting of two portions, apparently the maxilla 

 proper and an outer, slender i)alpus. 



