110 EXPLANATION OF THE FIGURES. 



Fig. 16. The same sac from the side. 



Fig. 17. The same sac seen from below ; , as in fig. 15. 



Figs. 18,19. Sac of Helicopsyche Shuttleworthi, Bremi. Natural size. 



Fig. 20. The same sac seen from above, enlarged. 



Fig. 2 1 . The same seen from the side, enlarged. 



Fig. 22. The same seen from beneath, enlarged. 



Figs. 23, 24. Valvata arenifera, enlarged and copied from Lea. 



Supplementary Observation. At my last visit to Zurich I saw in 

 Bremi' s collection the cases of a third larger species of Helicopsyche, 

 which Bremi obtained from Shuttleworth and has named Helicopsyche 

 Colombiensis. These cases come from Puerto-Caballo ; they have a 

 transverse diameter of 1^- lin. and a height of 1 T 2 ^ lin. Rhenish, and 

 are manufactured out of comparatively very coarse, rusty-brown stones. 

 With regard to Helicopsyche Shuttleworthi, Bremi informed me, that 

 the cases of this Phryganidous insect have now been found also on the 

 Lake of Geneva. 



PRINTED BY TAYLOR AND FRANCIS. 

 RED LION COURT, FLEET STRKET. 



