1910.] AND INVERTEBRATES OF ST. HELENA. 105 



time to time to attract the fish ; this bait the native fishermen 

 call " mince." The water is wonderfully transparent, and even 

 when there is no moon it is never quite dark. I was able to see 

 the bait on the hook to a depth of three fathoms, and there is no 

 doubt that the mackerel were able to see my nets and avoid them ; 

 the largest number I caught in the nets at one time was five. 

 These nocturnal habits explain why the eyes in Scomber colias 

 are so much larger than in S. scombrus, and this is therefore an 

 instance of a specific character which is adaptive. 



In my specimens the diameter of the eye is contained 3| to 3| 

 in the length of the head. The presence of the air-bladder may 

 also be adaptive, enabling the fish to adapt itself to great changes 

 of depth. The mackerel at St. Helena are mostly from 11 to 13 

 inches in length : the largest I measured was 13^ inches long and 

 weighed 1| lb. 



When I arrived at St. Helena at the end of February the 

 mackerel were nearly ripe, but I never obtained any quite ripe 

 and spawning, doubtless because they cease to feed for a time 

 when in this condition. In the material collected by the tow-net 

 were eggs with a single oil-globule, some of which probably 

 belonged to the mackerel, but I was not able to identify them 

 with certainty. After March 10th fewer mackerel were caught, 

 and on March 24th I opened a dozen in which the roes and milts 

 were small and collapsed and apparently spent ; I concluded that 

 these had recently spawned and that spawning takes place in 

 March. 



Mackerel are caught at St. Helena all the year round. In 

 February and March the fishing was carried on off a small island 

 called Egg Island near the western point of St. Helena, but 

 later in the year they are also caught off Jamestown and to the 

 east. They are always counted and sold in dozens ; sometimes 

 they bite very eagerly and are caught quickly, at others only 

 a few may be taken in a whole night. The largest number 

 caught by one boat during my visit was 59 dozen, the crew 

 consisting of six men. 



Genus Thynnus. 



Three kinds of albacore are constantly distinguished by the 

 fishermen of St. Helena, as was stated by Melliss in 1875 ; they 

 are called the long-fio, the bastard, and the coffrey, the first 

 being regarded as the typical form, and the term bastard being 

 used in the sense of variety, but the origin or meaning of the 

 third name I was unable to discover. The majority of recent 

 writers recognize only one species of long-finned tunny, the 

 Scomber ger mo of Lacepede, Thynnus alalonga of Cuvier& Valen- 

 ciennes. The revision of the Scombrida? of America and Europe 

 by Dresslar and Fesler, Bull. U.S. Fish. Comm. 1887, only recog- 

 nizes one species of long-finned tunny, which is named Albacora 

 alalonga, the common tunny being placed in the same genus as 

 Albacora thynnus. Jordan and Evermann, in ' Fishes of North 



