PANAMIC-PACIFIC PELECYPODA 59 



5. Shape corbuliform, the rostrum not clearly defined or without a sharp 

 border or rib. 



Subgenus Jupiteria 

 B. Shell large. 



6. Surface polished and marked by concentric and oblique lines on the 

 two sides. 



Subgenus Politoleda 



Subgenus SACCELLA Woodring, 1925 

 {Ledina Sacco, Dec. 1898, not Ledina Dall, April 1898.) 



Type species by original designation, Area fragilis Chemnitz (T=Leda 

 commutata Philippi). Miocene to Recent, Mediterranean. 



Shell generally small, the posterior side much narrowed, sharply pointed 

 at the end, the rostrum concave, wide, unicarinate or bordered by a sharp 

 ridge or rib. Hinge with the anterior and posterior set of teeth of nearly equal 

 length. Surface sculptured with fine or coarse concentrics. Posterior end 

 with a small, open gap. 



Thiele considered Saccella as a synonym of Jupiteria Bellardi 1875, 

 the type species of which [A^, concava (Born)] is a Miocene fossil from 

 Italy, Jupiteria is closely similar to Saccella differing mainly by its more 

 Corbula-\\\it shape and in having the rostrum less well defined, bordered 

 simply by a blunt or weak ridge. Several of our Pacific species could be 

 allocated to either section with equal reason. 



Key to Panamic-Pacific species of Saccella 



I, Shell strongly inequilateral, the posterior side much the longer, narrowed 

 and contracted, and produced into a sharply pointed end, 



A. Mostly quite small species (length 12 mm. or under), the anterior side 

 generally cut into by an impressed ray. 



a. Sculpture generally fine and uniform. 



1. Concentric riblets continuous over the whole surface from the anterior 

 submargins to the edge of the rostral keel. 



A^. ornata (PI. 2, fig. 3, 3a) 



2. Concentric riblets not quite continuous over the whole surface, often 

 partially smooth near the rostral keel. 



N.acrita{?\.2,i\g.7) 



b. Sculpture coarser and unequal. 



3. Shell rather depressed, the concentric riblets much larger, heavier and 

 more widely spaced in the middle zone. 



A^. impar (PI. 2, fig. 6) 

 II. Shell higher, the two ends more nearly alike in length, the posterior 

 side appearing short and stubby. 



B. Shell relatively large, 20 mm. or more in length. 



4. Sculpture formed by uniform, rounded, close concentrics between deeply 

 grooved interspaces. An anterior ray is often present. 



N. fastigata 



C. Shell smaller, 20 mm. or less in length. 



c. Concentric riblets are uniformly developed over the whole surface, 

 ca. Concentric riblets low, rounded and appressed, separated by incised 



lines only. 



