16 



THE VOYAGE OF H.M.S. CHALLENGER. 



The spinous dorsal commences above the gill-opening, is low and long, and formed 

 by seventeen slender spines. It is rather widely separated from the soft dorsal, whose 

 anterior connected rays form a short falcate lobe ; seven detached finlets follow. The 

 anal corresponds in position and form to the soft dorsal. These vertical fins can be 

 completely concealed in fissures on the back and abdomen. 



Pectoral fin short and powerful as in a short-finned Tunny ; ventral short, its root 

 opposite to that of the pectoral fin. 



Colour uniform steel-grey, lighter below ; caudal fin and inside of the pectoral 

 darker. 



Professor Hutton has taken the following measurements : — 



Total length, 

 Length of lieaJ, 

 Height of the body, 

 Thickness at the pectorals, 

 Breadth between eyes, . 

 Diameter of the eye. 

 Length of pectoral, 

 Longest dorsal spine, 

 Height of soft dorsal, . 

 Height of anal. 



The skeleton resembles much that of a Thynnus. However, the vertebrae are of a 

 less firm texture, somewhat porous, less deeply sculptured and lacking the high median 

 lateral ridge which is so conspicuous on the centrum of the vertebra of a Tunny. The 

 number of vertebras is twentj'-two or twentj^-three in the abdominal, and twenty-one in 

 the caudal division. None of the posterior caudal vertebrae are raised into the elevated 

 lateral ridge of the Tunnies. The arrangement and form of the neural, haemal, inter- 

 neural, and interhaemal spines are as in Thynnus, but all are more slender, as are also the 

 ribs and floating ribs. "Foramina inferiora"^ seem to be present in the zygapophysis 

 of the sixth to thirteenth caudal vertebraB. The hasmapophyses of the middle and 

 posterior abdominal vertebras coalesce to form a wide haemal canal, bixt whilst in 

 Thynnus the ribs are suspended from the extremities of the greatly prolonged 

 liaemapophyses of these vertebrae, they are, in this genus, attached to the base of the 

 apophyses. The neural spines of the seven posterior abdominal vertebras do not bear 

 interneurals. 



The skull differs considerably in having a high crest developed along the whole 

 length of its upper surface, but in other respects shows the closest agreement with that 

 of the Tunny. 



' Set Lutlieii, Vidensk. Selsk. Skriv., xii., 1880, p. 473. 



