August 18, 1911] 



SCIENCE 



217 



of the study and is a feature to be greatly 

 commended. 



Charles E. Bessey 

 University of Nebraska 



SPECIAL ABTICLES 



PROGEESSrVE VARIATION IN DECAPTEEUS, A GENUS 

 OF CABANGOID FISHES 



In the fishes of the genus Decapterus which 

 the writer has examined here and abroad, six 

 forms are recognizable, making a series from 

 species which perhaps belong rather to 

 Caranx, to the most extreme Decapterus. 

 Typical Decapterus departs from the Caranx 

 type in being less deep, less eoijipressed, in 

 having the last ray of the dorsal and anal fins 

 separate from the rest of the fin, forming a 

 mackerel-like finlet, and in possessing a 

 bluntly pointed protuberance with a groove 

 beside it, on the shoulder girdle under the 

 edge of the gill cover, suggesting a not dis- 

 similar structure in Trachurops, but less pro- 

 nounced. The most Carana;-like of the six is 

 Decapterus ajjfinis of the Pacific and Indian 

 Oceans. The four middle forms are inter- 

 mediates between this and the least Caranx- 

 like, D. macarellus. This progressive varia- 

 tion is readily explicable by a very attractive 

 theory of variation with migration, submitted 

 for what it is worth. 



The six forms are : 



1. D. affinis (Riippel). Figured by Day 

 (" Fauna British India, Fishes ") and Jordan 

 and Seale ("Fishes of Samoa,'' D. lundini). 

 Specimens have been examined in the British 

 Museum. 



Depth 3.5 in length to fork of caudal. Anal 

 soft rays 20-22. Lateral line with 50-63 

 scales followed by 42-47 scutes. Last ray of 

 dorsal and anal not detached from the rest of 

 the fin. Teeth small, evident. 



Range — ^Pacific and Indian Oceans. 



2. D. rhonchus (G. St.H.). A specimen ex- 

 amined in the Paris Museum. 



Depth 4.0. Anal soft rays 25-27. 56 scales 

 followed by 23-26 scutes in the lateral line. 

 Last ray of dorsal and anal not detached. 

 Teeth small, evident. Without the peculiar 

 shoulder structure mentioned above. 



Range — north and west coasts of Africa. 



3. D. maru-adsi (Temminck & Schlegel). 

 A specimen examined in the Paris Museum. 

 Cat. Fish, Brit. Mus. II. 



Depth 4.5. Anal rays 28. 50 scales fol- 

 lowed by 36 scutes in lateral line. Last rays 

 dorsal and anal detached from the remainder 

 of the fin. Teeth minute, evident. With the 

 peculiar shoulder structure. 



Range — Japan and China coasts. 



4. D. hurra (Cuv. & Val.). Day, Fauna 

 British India, Fishes. The type of D. hiliche, 



C. & v., examined in the Paris Museum. 

 Depth 5.0. Anal rays 26. 47-55 scales fol- 

 lowed by 33 scutes in lateral line. Last rays 

 dorsal and anal detached. Teeth minute, evi- 

 dent. Peculiar shoulder structure present. 



Range — Indian Ocean. 



5. D. punctatus (Ag.). Specimens exam- 

 ined in the Paris Museum labelled D. puncta- 

 tus and D. hurroides. Bull. 47, U. S. National 

 Museum. 



Depth 5.0. Anal rays 25. 56 scales fol- 

 lowed by 32 scutes. Last dorsal and anal rays 

 detached. Teeth minute, evident. Peculiar 

 shoulder structure present. 



Range — Atlantic Ocean. 



6. D. macarellus (Cuv. & Val.). Types of 



D. macarellus, pinnulatus, jacohmus and 

 scomhrinus, examined in the Paris Museum. 

 D. tnacarellus and D. sanctce-helenw. Bull. 47, 

 U. S. National Museum. 



Depth 5.5-6.0. Anal rays 28-31. 94-96 

 scales followed by 28-30 scutes. Last dorsal 

 and anal rays detached. Teeth not evident. 

 Peculiar shoulder structure present. 



Range — Atlantic and Pacific Oceans. 



Nos. 1 and 2 of this series would perhaps 

 fit better in Caranx than in Decapterus 

 (being more or less intermediate between C. 

 djedaha and the genus Decapterus). Speci- 

 mens of rhonchus and maru-adsi placed side 

 by side resembled one another very much, the 

 most noticeable differences being the imper- 

 fectly separated last dorsal and anal rays, 

 and absence of shoulder peculiarity in 

 rhonchus. Punctatus is much less compressed 

 than maru-adsi, and hurra intermediate be- 

 tween these two as is its range. These three 



