35 



CISTUDA BLANDINGII. 



Plate V. 



Characters. Head rather large, upper jaw emarginate in front, lower jaw 

 with a small hook; shell subround, elongated, smooth, ecarinate, with an entire 

 margin; sternum entire in front, deeply emarginate behind, bivalve, posterior valve 

 but slightly larger. 



Description. The head is rather large, smooth above, and slightly pointed at 

 the snout; the nostrils are anterior, and closely approximated; the eyes are large 

 and prominent, the pupil black, the iris light gray. The upper jaw is broad, the 

 cutting edge sharp and deeply emarginate in front; the lower is strong and firm, 

 and furnished with a small hook. The neck is long and slightly contracted at 

 the back of the head. 



The shell is oblong, rounded, very nearly as broad before as behind, smooth and 

 ecarinate, with an entire margin. Of the vertebral plates, the anterior is broad, 

 pentagonal, with two of its articulating surfaces directed forwards and outwards, 

 and meeting at an angle in front; the second and third are very regularly hexagonal, 

 broadest in the transverse direction — the former very slightly concave in front and 

 the latter as slightly concave behind; the fourth is regularly heptagonal, rather 

 concave posteriorly; the fifth is octagonal, smaller above and larger below. The 

 anterior lateral plate is irregularly quadrilateral, larger and rounded below, smaller 

 and straight above; the second and third are pentagonal; the fourth is smaller 

 and quadrilateral. There are twenty-five marginal plates, making an entire 

 cutting margin; the intermediate or nuchal is of moderate size and nearly a 



