14S Note on Certain Insect Larva-Sacs. 



operculum. But that the Helico])syche-sac$, are really produced by a 

 Phryganidous insect, I ascertained from the contents which I extracted 

 from two cases of Helicopsyche minima still furnished with opercula. 

 These consisted of a dried pupa, which in the form of the legs and of 

 the long antenna?, the four hairy rudiments of wings, and the two biting 

 jaws, exactly resembled a Phryganidan. The description given by 

 Lea of his Valvata arenifera (in his Observations on No jades and De- 

 scriptions of New Species, vid. Trans, of the Amer. Phil. Soc. vol. iv. 

 Philadelphia, 1834, p. 104, pi. 15, Fig. 36, a, b. See my copies, Figs. 

 23, 24) runs as follows : ' Testa orbiculata, convexa ; anfractibus tribus, 

 qui arenis agglutinatis operiuntur ; umbilico lato ; spira obtusa.' Hob. 

 — Cumberland River, near Nashville. Length four-twentieths of an 

 inch. Remarks. — This very curious and interesting species was among 

 the freshwater shells so disinterestedly sent to me by the Lyceum of 

 Natural History of New York, to be examined and inserted in this 

 paper. It has the singular property of strengthening its whorls by the 

 agglutination of particles of sand, &c, by which it is entirely covered, 

 and in this character it resembles Trochus agglutinans Lam. (T. conchy- 

 liophorus, Authors). The apex, in all the specimens which I have had 

 an opportunity of examining, is broken. The operculum was observed 

 in two specimens sufficiently perfect to exhibit a striated horny struc- 

 ture.' 



" The sacs of Helicop>syche minima communicated to me by Bremi, 

 agree almost perfectly with this shell of Valvata arenifera described 

 and figured by Lea. Even the bronze-green color is common to both 

 of them. The presence of an operculum is also in favor of the deriva- 

 tion of this habitation from a Phryganidous insect, as the sac-bearers 

 amongst the Lepidoptera form no operculum, but always spin down 

 their sac by its lower aperture to foreign substances. Moreover, the 

 opercula, of which I found several in my specimens of the sac of Heli- 

 copsyche minima, had also a striated appearance, like those of Valvata 

 arenifera. They were smaller than the aperture of the sac, and con- 

 sequently only closed it imperfectly. On examining them with the 

 microscope, I detected a fibrous structure in these opercula, arising from 

 comparatively coarse-spun threads, sticking close together ; at the mar- 

 gins of these opercula single threads protruded, by which they were 

 united with the mouth of the sac. In my specimens of the sacs of 



