822 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL.XX. 



northern K. glacialis (Leach) with which it was formerly identified. 

 It is a smaller, shorter, and more inflated species, with a shorter and 

 more sloping antero-dorsal margin and a more evenly curved ventral 

 margin, without the distinct antero-veutral indentation seen in that 

 species. The convex valve has a distinct, posterior radial ridge which 

 is faint or lacking in K. ///arm//*. There are also differences in the 

 hinge, in the right valve of the latter the teeth are more divergent, etc. 

 Doctor Carpenter, who established the group Kennerlia, defined it as 

 differing from typical Pandora in having an ossicle on the cartilage or 

 resilium, and radial grooves on the right valve. Perhaps the simple 

 linear form of the resilium in Kennerlia and its forked or V-shaped 

 form in true Pandora (type P. rostata Lamarck) may be of more impor- 

 tance. The intermediate ridge in the left valve of Pandora fits between 

 the two divisions of the V-shaped resilium. There is also in Kennerlia 

 a small, buttress-like projection within the margin, under the beak, 

 which supports an inward projecting portion of the ligament, darker 

 in color than the resilium. 



Family PERIPLOMIDJE. 



PERIPLOMA AFFINIS, new species. 

 (Plate LXXXVII, fig. 4.) 



Shell thin, fragile, broad ovate, with the beaks behind the middle 

 and with a short, narrowed posterior end. The antero-dorsal margin 

 is broadly convex: anterior end nearly evenly rounded, but slightly 

 produced in the middle; ventral margin evenly convex to the base of 

 the rostral region where it becomes slightly incurved; posterior end 

 much narrowed, compressed and produced into a short, blunt rostrum 

 with the edges gaping slightly at the end; postero-dorsal margin 

 nearly straight, sloping rapidly to the angle of the rostrum ; a faint 

 diagonal ridge extends to the lower rostral angle, posterior to which 

 the shell is smoother than elsewhere and marked with several faint, 

 radial riblets. The general surface is covered with irregular, uneven 

 and often rather faint, concentric undulations, separated by rather wide 

 concave intervals which, like the elevations, are covered by thin, 

 elevated lines of growth. The undulations are most regular on the 

 umbos and become less distinct and more irregular toward the margin 

 and anteriorly, and show by transparency on the interior of the shell. 

 The chondrophore is small, but very prominent, spoon-shaped, narrow 

 at the base and expanded distally, with a nearly round resilial pit. 

 The ossicle is well developed, bent into a crescent shape, and so formed 

 as to fit into the small rounded notch in the shell margin in front of 

 the choudrophores. A somewhat elevated submarginal ridge extends 

 forward from the notch and serves to support the thin ligament; a 

 similar but less prominent ridge extends backward from the choudro- 

 phores and defines a distinct ligamental groove. 



