241* LAKE SUPERIOR. 



surface, which gives the animal its Crustacean appearance, was firm- 

 ly adherent to the stone by its ciUated margin, and formed an excel- 

 lent protection under which the later transformations could take 

 place with safety. In fact, the superior shield being cast off with 

 the larva skin, served in place of the cocoon or nest constructed by 

 many larvae, before transforming. 



I regret that in the short account given by me at the recent 

 meeting of naturalists in Cambridge, I was induced to speak of this 

 discovery, without having access at the time to specimens. Those 

 which I expected to find at Boston had been lost, and my former 

 examination of the pupae collected by myself was very slight. I 

 referred the insect to the order of Neuroptera, and I must here 

 return my sincere thanks to my friend Dr. Harris, for a hint towards 

 its true nature. 



For the opportunity of examining some very large and well devel- 

 oped larvjB, I am indebted to my friend I. C. Brevoort, who procured 

 them at Niagara in July of the previous year. 



The body proper of the larvae is elongate, the head being free, 

 (i. e. not retractile,) but concealed under the large shield, like a pro- 

 longation of the dorsal epidermis of the prothorax. On each side 

 are six small, approximate ocelli, anterior to which is the antenna, 

 a little longer than the head, and two-jointed ; each joint having a 

 tendency to become divided at its middle, so that on a superficial 

 inspection there would appear to be four joints. These organs are 

 inserted at the outer extremity of the clypeo-cranial suture ; the 

 labrum is large, and a little emarginate in the middle. The lower 

 part of the head is covered by a large mentum, which prevents the 

 mandibles and maxillae from being seen. The maxillary palpi are 

 half the length of the antennae, filiform, rather stout, and three-articu- 

 lated, the joints being equal. The labial palpi are bent down and 

 covered by the epidermis. In the very young larvae the palpi are 

 still shorter in proportion to the antennae. A more full description 

 of the parts of the mouth must be reserved for a separate treatise, 

 when their structure can be illustrated by plates. The abdomen is 

 furnished on each side with six bunches of long branchial filaments, 

 which proceed from the interstices between the articulations ; there 

 is a larger bunch of filaments connected with the anal aperture, which 



