1892.] 



the latter species also has the intermediate and the posterior tibiae 

 curved. The male Coninomus nodifev has the hind tibiae widened and 

 notched just before the apex, and this sex of Anthicus instabilis has 

 the same limbs much widened towards the extremity. The male of 

 Heliopathes gibhus has the middle and posterior tibiae and the base of 

 the hinder femora fringed with long tawny hairs, which are absent in 

 the female. The males of some genera of weevils ( Cceliodes, Ceutlwrv- 

 kynchus, &c.) have the posterior tibiae furnished with a hook at the apex. 



(To be continued). 



MoUusca. — KTotes. 



NOTES ON VARIETIES. 



(Continued from page 155.) 



Overcrowding, or too limited a supply of water, has an injurious 

 effect on Limnaea stagnalis as well as on Homo sapiens. Semper shows 

 that these conditions, even when food is supplied in abundance, 

 produce du/arfed individuals, and such dwarfing cannot be com- 

 pensated afterwards by any especially favourable conditions or 

 treatment, as the shell is constructed on a more diminutive scale. 



Too Abundant Vegetation in water is considered conducive to 

 the formation of scalariform varieties of the genus Planorhis, "which 

 are often found in those bodies of water choked up with vegetation, 

 and according to Herr Clessin, also on the margins of lakes amongst 

 large stones. M. Van den Broeck considers this spiral form as a 

 modification consequent upon, and adaptive to the special peculiar 

 features of their environment, as he conclusively proved by experiment 

 that these spirally coiled shells make their way more readily through 

 the dense vegetation than those of normal shape which traverse the 

 thick masses of duckweed, &c., with great labour and difficulty." 



Unhealthy and Unnatural Conditions are also noted as 

 productive of distortions which are occasionally spiral, found in warm 

 water reservoirs, and in streams of water pumped from coal pits. Mr. 

 Taylor quotes a case in which nine-tenths of the L. peregva found one 

 season in a pool near Geneva had a curious malformation at the base 

 of the columella, which was coincident with an extraordinary 

 abundance of Hydra viridis in the pond. On the following year the 

 Hydra disappeared and the malformation ceased. 



Flowing and Stagnant Water.— Mr. S. C. Cockerell writing of 

 Limnaa has remarked that running water tends to foster a light and 

 slender form of shell, and stagnant water a stronger and more 



