218 AXEL A. OLSSON 



Length 58.5 mm., height 53 mm., diameter 31 mm. (type) 



This shell from Panama is related to C. distinquenda (Tryon) but is 



much less compressed, and has stronger concentric sculpture. Panama. 



Panama City on the reef off "French Plaza". 



Subgenus CTENA Morch, 1860 

 Type species by subsequent designation, Dall, Bartsch, and Rehder, 

 1938, Codakia pectinata Carpenter (not Gmelin) =C mexicana Dall. 

 Recent, Pacific coast of Mexico. 



Shell smaller than most species of Codakia, s.s., obliquely rounded, the 

 anterior side often the longer and generally convex. Lunule small, lenticular, 

 impressed, and more or less equal in both valves. Hinge of Codakia, s.s. but 

 with the posterior lateral tooth well developed. Surface sculptured by small 

 riblets beaded or decussated by the concentrics. 



Key to species of Panamic Ctena 



I. Sculpture elegant and neat, the radial riblets in the middle of the disk 

 small and finely cancellated, large and strong on the sides. 



1. Radial riblets developed over the whole disk. 



C. mexicana 



2. Riblets lacking on the dorsal slope, 



C. chiquita 

 II. Sculpture coarse and irregular, the riblets showing a tendency to 

 divide ventrally. Distribution more common southward of Panama. 



C. galapagana 



Codakia (Ctena) mexicana Dall Plate 29. figure 5 



Codakia (Jagonia) mexicana Dall, 1901, Proc. U. S. Nat. Museum, vol. 23, No. 1237, 



pp. 801, 822, pi. 40, fig. 6. 

 Codakia mexicana Dall, Maxwell Smith, 1944, Panamic Marine Shells, p. 57, fig. 720. 

 Ctena mexicana (Dall), Hertlein and Strong, 1946, Zoologica, vol. 31, pt 3, No. 8, 



p. 119. 



Shell small or of medium size (length up to about 22 mm., but usually 

 smaller), ovate-subcircular, the anterior side decidedly longer. Sculpture 

 neat and regular, formed in the middle of the disk by small, finely beaded 

 radials but considerably coarser on the anterior slope. Lunule large, 

 lanceolate, moderately depressed. 



Length 15.6 mm., height 14.8 mm., diameter 1.7 mm. right valve. 

 Acapulco, Mexico. 



Codakia (Cttna) galapagana Dall Plate 29, figure 8 



Codakia (Jagonia) galapagana Dall, 1901, Proc. U. S. Nat. Museum, vol. 23, No. 1237, 

 pp. 801, 823, pi. 40, fig. 4 Galapagos Islands. 



Shell small or medium sized (length 20 to 25 mm.), of medium con- 

 vexity, rather solid, white, rounded. It is similar to C. orbicvlata but has a 

 somewhat looser and more irregular ribbed sculpture, in which the radial 

 ribs have a stronger tendency to branch or divide as they approach the 

 ventral margin. The lunule is small, elliptical, impressed and nearly equally 

 divided between the two valves. 



Length 25.2 mm.; height 22.7 mm.; diameter 6.8 mm. left valve, Santa 

 Elena. Ecuador. 



