426 AXEL A. OLSSON 



Range — Coast of Peru northward to Panama. Panama: Pearl Islands. 

 Ecuador: Charapota; Santa Elena; Isla del Muerte. Peru: Zorritos; Lobitos; 

 Paita. 



Family COBBULIDAE 



The shell is small or medium size, rarely large, elongately ovate, usually 

 solid, the beaks generally submedian, the anterior side rounded, the posterior 

 side rostrated and pointed at the end. The right valve is usually larger and 

 with stronger sculpture, the left valve may be similar, or much smaller, 

 with a more rounded outline, its surface flat or depressed, and with finer 

 or smoother scu'pture. The ligament is entirely internal, attached to an 

 armlike resilifer in the left valve, simulating a large tooth and which fits 

 into a deep socket-like resilifer in the right valve. Hinge armature is 

 variable but most Corbulas have a single, large, hooked cardinal tooth in 

 the right valve placed in front of the resilial pit; there is a single cardinal 

 socket in the left valve; lateral teeth are absent in most groups. The pallial 

 line is entire or it may carry a small obscure posterior sinus. Surface covered 

 with a periostracum, sometimes heavy. 



Although the ligament of the Corbulidae, as in the Myacidae, is com- 

 pletely internal, the two bands of which it is composed, are attached to 

 separate scars. The armlike resilifer of the left valve carries two scars along 

 its upper surface; the larger scar on the inner or anterior side serves for 

 the attachment of the resilium; the other smaller one on the posterior side 

 for the tensilium. Both the resilium and tensilium have separate attachment 

 scars in the roof of the umbonal cavity of the right valve. 



The Corbulids are widely distributed and include marine, brackish, 

 and some fresh-water species, the latter mostly fossil. The family may be 

 divided into several subfamilies, based on characters of the hinge and liga- 

 ment, and on general habit. Most marine species belong to the Caryocor- 

 bulinae. 



Because of inadequate descriptions and small-sized figures, the identifi- 

 cation of a few Panamic species is somewhat uncertain and will remain so 

 until the types, if they are still extant, have been restudied and refigured. 



The Corbulidae may be divided into several subfamilies but only the 

 Caryocorbulinae is represented in the marine waters of the Panamic-Pacific 

 region. 



Subfamily CARYOCORBULINAE 



The chondrophore or resilifer is generally a large, projecting plate or 

 arm which simulated a cardinal tooth and is set obliquely to the hinge 

 margin of the left valve; it bears on its dorsal surface the attachment scars 

 of the tensilium and resilium. To this subfamily, belong the larger number 

 of marine Corbulas. 



Key to the genera of Caryocorbulinae in Panamic waters 



I. Valves more less similar in size, shape, and sculpture. 



A. Shell subovate, subrectangular to elongate in shape, the anterior end 

 rounded. The rostrum is relatively narrow and sometimes not sharply 

 defined. The posterior side is usually the longer, pointed or even twisted 

 at the end, often with a snoutlike extension formed by small, accessory, 

 shelly plates. 



