i8t;-j.] 117 



short, nearly of the same length; their breadth is that of the last thorac- 

 ic segment; the posterior ones however, are somewhat attenuated; the last 

 dorsal segment is trapezoidal, longer than the preceding; its posterior mar- 

 gin is sinuated. 



An almost imperceptible longitudinal impressed line runs along the 

 middle of the dorsal side of the body, on the thoracic and abdominal seg- 

 ments. 



This larva shares all the striking characters of the larvae of Cyphon^ as 

 characterized by Erichson (see Chapuis & Candeze, Catalogue des larves 

 etc. p. 493, tab. V, fig. 5); the long antennte, the rounded labrum, excised 

 anteriorly, the long maxillary palpi, the large labium, with the labial pal- 

 pi very distant from each other etc.. are common to both. If my descrip- 

 tion of the lingua and the maxill;\! is less detailed than that of this author, 

 it is merely because, having only a single specimen for examination, I did 

 not like to dissect it. No more than Erichson did I perceive any vestiges 

 of stigmata. 



The differences which I observe consist in the form of the head, which, 

 in my specimen, is less expanded behind the antennae and in the more 

 considerable length of the latter. 



To the discoverer of the larva, Benj. D. Walsh Esq., in Rock Island, 

 111., I am indebted for the following notice about its habits :- 



'' The larvfe of Prionoci/plio)) {fisroidcns Say, occurred abundantly of va- 

 ••rious sizes about the end of .May in the hollow of an oak stump contain- 

 •' ing a gallon or two of water. Some were in the decayed wood which 

 '• formed the walls of the hollow, but most of them were attached to pieces 

 " of loose wood and bark which lay at the bottom of the water. The 

 " pupae appeared to be found only in the walls of the hollow. 



'• On the 7th of June, having given a fresh supply of the coffee-colored 

 " water from the stump to a number of these larvae, which I had placed 

 •• in a glass iar, I noticed them beneatli the surface of the water vibrating 

 '• vigorously up and down a pencil of hairs proceeding from a horizontal 

 •'slit in the tail. This pencil appeared to be about the length of four ab- 

 ■'dominal segments; and on a subsequent occasion, one of the larvae hav- 

 •' ing suspended operations for a second or two. T was able to see. with the 

 ••assistance of a double lens magnifying about four diameters, that the 

 ••pencil was composed of three pair of filaments, each beautifully bipecti- 

 •■ nate. I presume it is used to extract air from the water. 



" When at the surface this larva generally, but not ahvays. swims on its 

 ••back, keeping its body slightly below the surface and striking with its 

 •• feet, .so as to jerk from point to point in a cui'ved line. The pencil of 



