﻿392 



PROCEEDINGS OF THE NATIONAL MUSEUM 



3a. 



36. 



Mandible long, nearly ji length of head; scales around caudal peduncle 

 20 to 26; dorsal rays usually 13 (12-14). Atlantic drainage of Lakes 

 Managua and Nicaragua, Nicaragua chavesi 



Mandible short, less than Ys length of head; scales around caudal peduncle 

 28 to 31; dorsal rays usually 11 or 12 (9-13, rarely 9, 10 or 13). 

 Paciiic slope of northwestern Mexico (Sonora and Sinaloa) smithi 



DOROSOMA CEPEDIANUM (LeSaeur) 



Megalops cepediana LeSueur, 1818, pp. 361-363 (original description). 



This wide-ranging species is a common inhabitant of the fresh and 

 bracldsh waters of eastern North America. According to a recent 

 study by Gunter (1945, pp. 30-31 and table 74), it spawns in fresh 

 water, and often frequents brackish water, but only rarely enters the sea. 



Diagnosis. — A Dorosoma with 48 to 51 (usually 50) vertebrae,^ 52 

 to 70 lateral scales, 36 to 45 scales around the body, usually 12 dorsal 

 rays, 25 to 36 (usually 29 to 34) anal rays, preponderantly 18+12 

 ventral scutes, and with a long dorsal filament. 



Table 2. — Fin-ray counts in four species of Dorosoma 



[The figures in the first line for each count are the observed range and, in parentheses, the mean; the figure in 

 the second hne represents the number of specimens] 



Variation. — Counts of fin rays, scales, and ventral scutes were made 

 on 51 to 200 specimens distributed from Michigan and Maryland 

 southward and westward to Tamaulipas, San Luis Potosi, and 

 Queretaro, Mexico (tables 2-4). There seems to be no correlation 

 between the counts and geographic regions, but the material examined 

 was so widely scattered and the number from any one locality so few 

 (maximum 9, usually 2 to 5) that potential gradients may have been 

 masked. A thorough study of variation in this species is needed. 



As in the other species of the genus, the length of the dorsal filament 

 varies greatly with age (see section on "Changes with Growth")- 

 Statements regarding this structure are therefore meaningless unless 

 accompanied by data on the size of the specimen. 



8 In response to my query. Dr. Vladykov wrote that the number of vertebrae he recorded (1945, p. 35) for 

 this species was a typographical error and should have read 51 (29+22). 



