SPH^RIUM. 11 



rather strong ; teeth arranged as in the other species, but 

 the cardinal teeth are smaller and the lateral ones shorter in 

 proportion : muscular and pallial scars scarcely perceptible. 

 L. 0-3. B. 0-4. 



Var. 1. JBrochoniana. Shell much larger and flatter; beaks 

 smaller and less prominent. S. Brochonianum, Bourguignat, 

 Monogr. p. 20, pi. 3. f. 1, 2, 3. 



Var. 2. rotunda. Shell rounder and flatter; epidermis yel- 

 lowish-green. 



Var. 3. Ryckholtii. Shell small, triangular, and globular; 

 beaks very prominent. C. Ryckholtii, Norm. Cycl. p. 7, f . 5, 6. 



HABITAT : Lakes, ponds, and canals, and stagnant 

 water everywhere in England, Wales, and Ireland ; but 

 I have not observed it in Scotland, nor seen any notice 

 of its having been found there. Var. 1. Clumber lake, 

 Notts (J. G. J.). This considerably exceeds the usual 

 form in size, being in length 0*45, and in breadth 0*6, 

 although its depth or thickness is only 0*25. Var. 2. 

 Singleton, near Swansea (J. G. J.). Var. 3. Marsh be- 

 tween Exmouth and Budleigh Salterton (J. G. J.). In 

 another piece of stagnant water near Exmouth a small 

 globular variety occurs, in which the beaks are not pro- 

 minent. A monstrosity is also sometimes met with, in 

 which the lower or front margin is constricted or divided 

 by a groove. Mr. Kenyon found it in the North of Eng- 

 land; and I have also taken it in Crymlyn bog, near 

 Swansea. Some shells, which Mr. Choules has found 

 near Richmond, partake of the characters both of this 

 species and 8. ovale, and apparently form an interme- 

 diate link between them. According to Middendorff this 

 species inhabits Siberia ; and Philippi and Terver have 

 recorded it from Sicily and North Africa. It has also a 

 wide range in the intermediate parts of Europe. It 

 often occurs in company with 8. corneum ; and I have 

 found it alive in the hardened mud of a pond which 

 had been drained and its bed so completely dried up 



