24 GEO. H. HORN, M. I). 



are two or three shorter ones arising close to the posterior margin of 

 the segment and directed backwards ; across the middle of each seg- 

 ment (except the last) a row of short spines. Anal fissure with a 

 process each side, bisetose at apex. 



Legs short and stout, widely separated, the coxa oval, femur more 

 or less quadrate in outline, tibia more cylindrical, terminated by a 

 single strong claw. Anterior femur obtusely subangulate beneath. 

 The edges of the articulations with spinules gradually shorter to the 

 tip of tibia. PI. iii, figs. 21-22. 



Spiracles. — There are nine pairs of spiracles. The first pair is 

 situated at the side of the mesosternal segment close to the anterior 

 angle in a fold between the dorsal and ventral plates. The abdomi- 

 nal spiracles are in the first eight segments on the dorsal side just 

 within the position of the short lateral spine. The last spiracle is, 

 however, nearer the angle than the others. 



The larva just described is, in form, like that of a slender Silphide, 

 recalling also the Corylophidte, but too little is yet known of the 

 larvie of many genera to which Platypsylla is supposed to be related 

 to enter into any generalizations. 



It is well known that no mandibles have been detected in dissections 

 that have been made of the imago, but in the larva we have very 

 distinct mandibles which are probably lost in the last moult of the 

 larva to the pupa state. By comparison it will be seen that the 

 buccal cavity is similar in outline in the larva and imago. 



The maxillae are soft in structure and give no evidence of the 

 future form of those of the imago. 



The largest of the larvpe seen is not longer than 1.6 mm. and is 

 probably not fully grown, seeming rather disproportionate in size to 

 the future imago. It must not be supposed that a small larva pre- 

 supposes a small imago, as the larva of Diccelns purpvmtus would 

 never be suspected of yielding the large imago without actually raising 

 the larva to maturity. 



For great assistance in the determination of the position of the 

 spiracles I must acknowledge my indebtedness to Prof C. V. Riley, 

 who has also, for some time, had this larva under consideration. By 

 means of stained specimens and photography the entire structure has 

 been very accurately developed. 



The larvte in Prof Riley's hands vary in size (like my own) from 

 1.2 to 1.7 mm. and were obtained from a Beaver trapped by Mr. 

 Lawrence Bruner at West Point, Neb., October, 1886. 



