Note on Certain Insect Larva-Sacs. 147 



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

 as the dimensions, remind one strikingly of the Valvata depressa Pfr. 

 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 opercula exhibited, besides the spiral or 

 regularly concentric structure above referred to, an excentric longitudi- 

 nal 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 shejl and operculum. 

 In Reaumur's Memoires pour servir a V Histoire 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 oper- 

 culum.' 



" The case last referred to by Shuttleworth 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 Shut- 

 tleworthi 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 Hellcopsyche 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 

 Shuttlcworthi is 2 lines (Rhenish), and of those of H. minima 1 line. 

 A principal distinction between these Phryganidan 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, polygo- 

 nal particles of sand, closely cemented together from within and with- 

 out. The caterpillars of Psyche also never close their sacs with an 



