48 



PROCEEDINGS OF THE NATIONAL MUSEUM 



what they are in the percoids. In the percoids, the pectorals may be 

 used to govern the vertical plane of forward movement, for stopping, 

 turning, "treading water," and even in some — -e.g., the labrids — for 

 forward locomotion. One of the structural features that permits all of 

 these activities is the ability to rotate the pectoral base around 

 the upper ray as an axis. In the percoids, the uppermost pectoral ray 

 articulates with the scapula (as in fig. 11a), but the lower rays articu- 

 late with progressively longer and independently movable actinosts. 

 (If the outer ends of these actonosts are swung outward and downward, 

 the pectoral fin base is brought into a plane vertical to the water; if 

 they are swung up and back, the fin base moves toward a horizontal 

 plane.) Among all but the most generalized of the Blennioidei (fig. 

 11a), both the function and structure of the pectoral change consider- 



Figure 11. — Primary pectoral girdle, right side: a, Prolatilus jugularis; b, Hemerocoetes 

 species; c, Labrisomus nuchtpinnis. (In each figure, position of base of uppermost pectoral 

 ray is shown.) 



ably. These fins (except in tropical blennies), instead of being used in 

 maneuvering, may act as props against the bottom and, by being 

 brought back sharply against the body from a somewhat erect position, 

 may provide a fast standing start from the normal stationary position. 

 Structurally, the pectorals of the Blennioidei, except where secondar- 

 ily reduced as in the Congrogadidae, almost always are rounded and 

 broad based. The pectoral girdle tends to have broad actinosts rigidly 

 attached to the scapula and coracoid and to one another in order to 

 form a rather rigid, platelike surface of attachment for the pectoral 

 rays. In one group of the Blennioidei, the Notothenioidae, the plate- 

 like nature of the primary girdle frequently has been increased 

 further by the fusion of the uppermost actinost with the scapula, re- 

 ducing the autogenous actinosts to three. This has occurred in the 

 Bovictidae, Nototheniidae, Harpagiferidae, Bathydraconidae, Chan- 

 nichthyidae, and the trichonotid (sensu lato) Hemerocoetes (fig. 116). 



