194 1 CATALOGUE OF FISHES OF TORTUGAS 287 



In 10 specimens from Tortugas the soft rays in the dorsal vary from 27 to 28, 

 and in the anal from 24 to 26. 



The dark shades or blotches along the back, described in living or fresh 

 specimens, remain in the preserved material, and are present even in the smallest 

 specimens at hand. The forked or V-shaped one under the anterior part of the 

 soft dorsal is the most prominent, and forms a ready recognition mark. Some, 

 but not all, of the young have greenish or pale spots along the back, which more 

 usually are present and more distinct on the posterior parts of the soft dorsal and 

 on the anal. 



The following account of the structure and operation of the peculiar spinous 

 dorsal of B. capriscus was prepared partly from Dr. Longley's notes and partly 

 from whole and dissected specimens in hand. 



The spinous dorsal of this and related species is a mechanism so widely appre- 

 ciated in its operations that the generic names Batistes and Balistapus and the 

 common name "triggerfish" have all been suggested by it. 



The hard parts of this mechanism consist of 3 spines and a bone which forms 

 a trough. The spines are set in this trough, beneath which their basal elements 

 project. The 1st spine, near its base, is attached to the head in advance of it by a 

 pair of strong muscles lying on each side of an occipital crest and extending 

 forward well beyond the eyes. These muscles obviously are the erectors of the 

 fin. Next, the 2d spine is bound to the 1st by several strands of connective tissue 

 that extend from well above the base of the 2d more or less horizontally to the 

 deep posterior groove of the 1st spine. Finally, the 3d spine is bound to the 2d 

 by a single strong strand of connective tissue that reaches from near mid-length 

 of the 3d spine to near the base of the 2d. In small specimens, at least, the strands 

 of connective tissue between the spines generally can be seen lying within the 

 interradial membranes. Because the 2d and 3d spines are bound to the 1st, they 

 must follow the 1st when it is erected. 



The locking of the spines occurs when they are erected, as the 2d spine is 

 drawn forward, and the slight knob on the anterior margin of its base slips into 

 the deep posterior groove of the 1st spine, which with its edges is bent forward 

 rather sharply near the base of this spine. In other words, when the 1st spine is 

 erected the base of the 2d spine is drawn forward into a space partly under the 

 base of the 1st. The basal knob fits into the base of the groove of the 1st spine so 

 snugly that it "locks" it securely. The 1st and 2d spines, then, cannot be deflexed 

 until the base of the 2d is drawn backward, and out of the partial socket under 

 the 1st. As the 3d spine is attached to the base of the 2d by a strand of connective 

 tissue, the base of the 2d slides backward quickly if the 3d spine is deflexed. 

 Therefore, the 3d spine forms the "trigger," making it impossible to unlock the 

 other 2 spines without depressing the 3d. 1 



Both coasts of tropical America; entire Atlantic coast of the United States and 

 southward. S. F. H. 



1 Since the above was written, an article by Charles R. Clothier (Calif. Fish and Game, 

 vol. 25, no. 3, 1939, pp. 233-236, figs. 86-89) describing the bony structure of the locking 

 mechanism of the Pacific triggerfish, Capriscus polylepis, has appeared. This mechanism 

 seems to be virtually identical in the two species in which it has been studied. — S. F. H. 



