4 SPHjERIIDyE. 



Var. 4. Pisidioides. — " Shell subtriangular, and rather more 

 produced at its posterior slope ; transverse (or concentric) striae 

 coarser ; ligament slightly perceptible on the outside. Grand 

 Junction Canal at Paddington. A form approaching this variety 

 has been taken by Mr. Jordan near Bath, and by Mr. Nelson 

 near Birmingham." — B.C. Regent's Park, and Brentford, Essex 

 (Rich). The Rev. J. McMurtrie informs me that " this variety 

 or one resembling it is abundant in the canal at Edinburgh, 

 where the ordinary form does not occur. The ordinary form is 

 the only one found in other pieces of water in the neighbourhood 

 of Edinburgh." 



2. S. Rivi'coLA,* Leach. Pl. I. 



Body grey, tinged with yellow or brown ; foot broad, some- 

 what swollen towards the extremity, greyish-white ; mantle dark 

 grey at the edges ; gills brownish or reddish-grey ; sipho7is of 

 nearly equal length, short, whitish. 



Shell oval, swollen, sides nearly equal, solid, glossy, yellowish- 

 brown, occasionally with a greenish tinge, frequently encircled 

 with bands of a darker colour ; with strong concentric ridges 

 which are crossed by fine stri^ ; epidermis thick ; ajiterior side 

 rounded ; posterior side somewhat produced and truncated ; 

 beaks obtuse, central ; liga77ient short, conspicuous ; inside 

 pearly ; hinge and teeth as in .5". corneum, but stronger ; scars 

 distinct. 



Inhabits sluggish streams and canals in the 

 home, midland, and some of the northern counties of 

 England. In Ireland it has been found near Dublin, 

 but it is a local species. It differs from 5. cornetim 

 in being much larger and more solid, as well as in its 

 oval form and strong ridges. Near Bath (Daniel), 

 B.C.y vol. V. p. 150. River Cherwell, Banbury, Oxon 

 (D. Pidgeon), near Blue Bridge, York (Hey), J.C, 



* Inhabiting brooks. 



