FINS. 



43 



rays, the outer of which is frequently osseous. In some small 

 groups of fishes, like the Gobies, the fins coalesce and form 

 a suctorial disk. 



Fig. 6. — Salmo salar (Salmon), with abdominal ventral fins. 



Fig. 7. — Mullus barbatus (Red Mullet), with thoracic ventral fins. 



"'S'^^ls '^S&i 



Fig. 8. — Burbot (Lota vulgaris), with jugular ventral fins. 



For the definition of the smaller systematic groups, and 

 the determination of species, the numbers of the spines and 

 rays are generally of the greatest importance. This holds 

 good, especially for the ventral rays, by the number of which 



