Page:An Introduction to the Study of Fishes.djvu/67

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.

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