204 Nelson on Tertiary Mollusca of Peru. 



10 millim. Beak, elevated, large; cardinals quite curved and diver- 

 gent. 



Length 45 millim. ; breadth 41 millim. 



Hemicardia affinis, sp. nov. 



Two specimens were found, belonging to this genus, and related to 

 S. ohovalis Carp., but may easily be distinguished from that species 

 by the following differences. Ribs much finer, more elevated, and 

 the spaces between them broader. The two species differ also in the 

 proportional measurements. 



Length 19'1 millim. ; breadth 10-4 millim, ; height 10 millim. 



Area Larkinii sp. nov. 



Plate VII, figures 5, 6, V. 



Shell thick and heavy. Anterior extremity short and rounded; 

 jiosterior more or less produced. Beaks widely separated, raised and 

 very prominent. Ligament area large, about half as broad as long. 

 Surface marked by from 30 to 33 radiating ribs, which are rounded 

 and broader than the spaces between them. Ribs ornamented by 

 rounded tubercles and crossed by numerous fine lines of growth. 

 Teeth numerous, strong, nearly straight, equidistant, except at the 

 extremities of the hinge line, where they become divergent and much 

 stronger. The margin of the shell is deeply scalloped by the extremi- 

 ties of the exterior ribs and grooves. Just above the marginal teeth 

 the inner surface of the shell is marked by fine radiating lines, from one 

 fourth to one half of an inch in length. Anterior muscular scar 

 almost circular ; posterior elongated and narrow. 



Length 27'4 millim.; breadth 29*6 millim.; height 25*8 millim; be- 

 tween umbos 5*8 millim. 



The specimen, whose measurements are given above, is the largest 

 perfect one, and perhaps the most characteristic. 



Fragments and single valves of much larger specimens are abun- 

 dant. A large specimen gives the following approximate measure- 

 ments: length 35-4 millim.; breadth 37'4 millim.; height 35 millim.; 

 between umbos 8 millim. 



This species bears strong analogy both to Area grandis Brod. and 

 Sby., and Area tuberculosa Sby. It agrees with the former in general 

 habit of growth, with the latter in form and tuberculose characters 

 of the ribs. It may, however, be distinguished from A. grandis by 

 its more numerous, rounded ribs, less ci'owded teeth, and more oblong 



