PANAMIC-PACIFIC PELECYPODA 103 



Bucaro. Colombia: Isla del Gallo. Ecuador: Esmeraldas; Sua; Cabo Pasados; 

 Manta; Manglaralto; Santa Elena; Ancon. Peru: Zorritos; Punta Picos; 

 Mancora; Negritos. 



Genus SHELDONELLA Maury, 1917 



Type species by monotypy, Noetia (Sheldonella) maotca Maury. Mio- 

 cene of Santo Domingo. 



Shell small, modioliform, thin or subsolid, the posterior side widely 

 expanded. Posterior-umbonal slope is strongly convex or vaulted, the 

 ventral side below it usually impressed. Beaks small, nearer the anterior 

 end, slightly opisthogyrate. Cardinal area is an elongate, flat zone of moder- 

 ate width distributed along the hinge line; the ligament itself being re- 

 stricted to a triangular area under the beak almost equally divided between 

 the anterior and posterior sides, the extreme posterior half of the cardinal 

 area being bare. The area of the ligament is vertically grooved. Sculpture 

 is formed of numerous, small ribs, their interspaces with a smaller inter- 

 stitial riblet. Ventral margins closed, without a byssal gap. 



The smaller species of Eonotia such as A^. olssoni and N. centrota bear 

 resemblance to Sheldonella in their hinge characteristics and sculpture but 

 they differ notably in shape and in possessing a strong, umbonal angle. 



Sheldonella delgata (Lowe) Plate 10, figures 3, 3a 



Area delgada Lowe, 1935, Trans. San Diego Sec. Nat. Hist., vol. 8, No. 6, p. 16, pi. 1, 



fig. 2. 

 Noetia (Sheldonella) delgada (Lowe), Reinhart, 1943, Special Paper, Geol. Soc. America, 



No. 47, pp. 77, 78, pi. 12, figs. 3-5.— Hertlein and Strong, 1943, Zoologica, vol. 



28, pt. 2, p. 163. 



Rare and local. This species is similar to S. maoica Maury from the 

 Miocene of Santo Domingo. The Panama specimens were obtained from 

 shell drift collected along the east shore of the Burica Peninsula. 



Range— Mexico southward to Panama. Mexico: Manzanillo (Lowe), 

 also Hertlein and Strong. Panama: near Punta Piedra south of Puerto 

 Armuelles. 



Family OLYCYMEKIDAE 



Shell usually solid, porcellaneous, equivalve, with subcentral umbones 

 and small prosogyrous or opisthogyrous beaks above a well-defined cardinal 

 area, the valves generally quite convex, subcircular, subovate to subtrigonal 

 in shape, generally slightly inequilateral, the anterior side is usually more 

 evenly rounded while the posterior side is often somewhat narrowed and 

 angulated, the valve margins closing tightly. The hinge plate is arched and 

 bears numerous chevron-shaped taxodont teeth on each side, the teeth 

 smaller in the middle zone and often partly or completely obliterated there 

 by the downward spread of the cardinal area. The cardinal area may be 

 narrow or high, subtriangular in shape, usually more or less equally de- 

 veloped on each side of the beak, or the posterior side may be much longer, 

 its surface deeply engraved by tent-shaped grooves, the whole covered by 

 a dark-brown ligament. Adductor scars usually well marked, subequal, 

 often elevated and connected by an entire pallial line lying just withm 

 the ventral margin. Surface smooth or radially sculptured, the ventral 

 margin smooth but more often furrowed. Periostracum thin or almost absent 

 or heavy and densely pilose. 



