SAC-BEARING LEPIDOPTERA. 29 



atecl its faeces, it pushes them out of this aperture, when the 

 edges of the latter rise a little. This lateral opening of the sac 



here literally. The passage in question runs as follows: "Amongst the 

 Mollusca collected by Blauner in Corsica, there was a considerable number of 

 a shell, which was at first taken for an undescribed species of Valvata, and 

 which appeared to be nearly allied, if not identical, with the Valvata arenifera 

 of Lea (Observ. p. 114. tab. 15. figs. 36 a & b], from North America. The 

 perfectly regular, spirally convoluted shell consists of a very fine transparent 

 membrane, upon which very small grains of sand and stones are fixed with the 

 greatest regularity. The circular orifice is closed by a very delicate, appa- 

 rently spirally convoluted, membranous operculum. The general form, as well 

 as the dimensions, remind one strikingly of the Valvata depressa, Pf. In all 

 the individuals provided with an operculum, there was either the larva or the 

 nympha of an insect, probably belonging to the genus Phryganea, which, bent 

 into a half-spiral, lay singly in each shell. Under the microscope, the oper- 

 cula exhibited, besides the spiral or regularly concentric structure above 

 referred to, an excentric longitudinal opening running parallel to the inner 

 margin. Specimens of the Valvata arenifera of Lea, which I have recently 

 obtained from Vienna, exhibit precisely the same structure both of the shell 

 and operculum. In Reaumur's Memoires pour servir a VHistoire des Insectes, 

 torn. iii. p. 193. pi. 15. figs. 22-24, there is a short description and figure of a 

 (spirally-convoluted) Phryganea-case (occurring in Switzerland). This species 

 of Reaumur's, however, differs in every other particular from the species above 

 described, and also appears to possess no operculum." The case last referred 

 to by Shuttlevvorth belongs to Psyche Helix ; the other one, which resembles 

 a Valvata, on the contrary, is a very different thing (see my figures 18-22), 

 and is certainly produced by a Phryganidous insect. I saw several of the 

 habitations of this insect in Bremi's collection at Zurich, partly collected in 

 Corsica and partly on the Lake of Como. Bremi has given the name of 

 Helicopsyche Shuttleworthi to the questionable Phryganidan from which 

 these spiral cases are derived ; and many specimens of a similar smaller case 

 have been since sent to him from a brook in Porto Rico, the inhabitant of 

 which Bremi has named Helicopsyche minima. By the kindness of Herr Bremi 

 I have obtained several specimens of both kinds, which are essentially different 

 in their structure from the sacs of Psyche Helix. As regards their size, the 

 diameter of the largest sacs of Helicopsyche Shuttleworthi is 2 lines (Rhenish), 

 and of those of H . minima 1 line. A principal distinction between these Phry- 

 ganidan domiciles and the spiral sacs of Psyche consists in the fact, that whilst 

 in the case of Psyche Helix extremely fine grains of sand are stuck as a coating 

 upon the outer surface of the white web of the sac-walls, in Helicopsyche the 

 walls of the habitation are formed directly and solely of larger, polygonal par- 

 ticles of sand, closely cemented together from within and without. The cater- 

 pillars of Psyche also never close their sacs with an operculum. But that the 

 Helicopsyche-s&cs are really produced by a Phryganidous insect, I ascertained 

 from the contents which I extracted from two cases of Helicopsyche minima 



