98 



it a variety of U. complanatus, but a re-examination 

 of the specimens has led me to regard it as a distinct 

 species. It is proportionally longer, and may always 

 be recognised by its elevated ligament margin, and 

 the remarkable inflation of the upper part of the 

 umbonial slope. The sinus of the cartilage is much 

 shorter than in the variety of the allied species which 

 it most nearly resembles, (U. cariniferns, Lam.) the 

 posterior margin more oblique, and the umbo is much 

 wider; it has also more robust and much less promi- 

 nent cardinal teeth; a much smoother and less 

 wrinkled epidermis, and the interior is never dark 

 purple. 



UNIO ANGUSTATUS. 



Plate LIV.— Fig. 2. 

 DESCRIPTION. 



Shell elliptical, elongated, ventricose; disks slightly 

 contracted obliquely from beak to base; ligament and 

 basal margins parallel; anterior dorsal margin ele- 

 vated, obtusely rounded at tip; posterior margin 

 rectilinear, profoundly oblique; extremity obliquely 

 truncated, the inferior angle or tip acute; considera- 

 bly above the line of the base; umbonial slope angu- 

 lated, rectilinear; beaks decorticated, slightly promi- 

 nent, acute, approximate; basal margin slightly 

 contracted in the middle, epidermis brown olivaceous, 

 obscurely rayed; within pale chocolate colour and 



