CLASSES, ORDE'RS, ETC. 



6l 



nearly central \ ligament short, not visible from the outside. 

 Length if lines; width i| lines. Marshes and ditches. 



P. pusillum? . 



(d) Shell suborbicular, in the upper part rather tumid, in all 

 the other parts compressed, thin, very glossy ; ligament short, not 

 visible from the exterior ; muscular impressions distinct. Length 

 Y^th inch ; width ith less. Ponds and pools. P. nitidum? 



(e) Shell very small, oblong, thin, ventricose, deeply striated, 

 yellowish-white or pale horn-coloured ; umbones blunt, prominent, 

 very excentric ; ligament nearly invisible ; muscular impressions 

 indistinct. Ponds and pools. P. roseum. 



Family II. Unionidse. 



Shell large, oblong, equivalve, inequilateral. Mantle lobes free 



Fig 27. Unio Plctorujn, 



/ 



all round, except at the posterior edge, where they form two 

 orifices, which are somewhat awl- shaped. 



5 v. ventrosa, shell slightly more trigon-shaped, more ventricose, v. grandis, 

 much larger, v. obtmalis, shell smaller, much more tumid, umbones sharp and 

 pronounced. 



c v. sphndens, lemon-coloured. 



