Mltl 



dorsal spine in some balistids (especially Rhinecanthus) 

 has its anterior face well ornamented with relatively 

 large barbs, while some monacanthids have the first dor- 

 sal spine absolutely smooth. The first dorsal spine of 

 balistids serves, among other defensive functions, to 

 wedge the fishes into holes and cavities that they seek 

 out in danger and in rest. I suspect that the first dorsal 

 spine in most monacanthids is used less in this manner 

 and more as a rapid vibrator in communication during 

 agonistic and breeding behavior. In some monacanthids 

 the spine can be vibrated back and forth with such speed 

 that it blurs before the eyes. 



The typical crushing dentition of balistids has been 

 converted in monacanthids to more of a nibbling form, 

 while the massive supporting structures of the balistid 

 jaws give way in monacanthids to a much more delicate 

 suspensorium, the palatine being reduced in size and less 

 intimately connected with the ectopterygoid, and the 

 ethmoid and parasphenoid far less massive. The pharyn- 

 geal apparatus of balistids is changed in monacanthids 

 by the loss of the suspensory pharyngobranchial, the loss 

 of teeth on the fifth ceratobranchial, and the usual loss of 

 the second branchiostegal ray. 



A balistidlike pelvis is found in the more generalized 

 monacanthids, although it usually is not quite so mas- 

 sive as in balistids. However, the main difference 

 between the pelvic apparatus in balistids and generaliz- 

 ed monacanthids is in the reduction in the size of the 

 rudimentary fin ray (or spinous element) at the end of 

 the pelvis and of the number of series of specialized 

 scales surrounding it. In all balistids there are four series 

 of encasing scales, and in all but Canthidermis these 

 series have a dorsoventral flexibility. In the great majori- 

 ty of balistids the rodlike ossification extending pos- 

 teriorly from the end of the pelvis, representing a com- 

 pound formed from a right and left rudimentary and 

 highly modified fin ray or spine (see Tyler 1962b) of the 

 otherwise absent pelvic fin, exits through a foramen in 

 the fourth and last segment of encasing scales to 

 protrude to the exterior. The compound rod usually is 

 branched distally, although it has lost its segmentation. 

 This is the condition found in the various species ex- 

 amined of Batistes, Balistoides, Abalistes, Hemibalistes, 

 Balistapus, Rhinecanthus, Sufflamen, and Odonus. Of 

 the two species of Xanthichthys examined, the ray is like 

 that in most other balistids in X. ringens, but in X. 

 lineopunctatus the ray is shorter, and, while branched 

 distally, it does not protrude to the exterior and there is 

 no foramen in the last series of encasing scales in the 

 single large (181 mm) specimen examined. Since the ray 

 itself is similar in X. ringens and X. lineopunctatus other 

 than the shorter distal portion in the latter, it is possible 

 that small specimens of X. lineopunctatus have the ray 

 protruding through a foramen which eventually closes 

 over while the distal portion of the ray is resorbed. 

 However, I have no small specimens of the relatively 

 rarely collected X. lineopunctatus to examine for this. In 

 both of the two species of Melichthys examined the fin- 

 ray element is a large cone-shaped ossification represent- 

 ing only the anterior end of the element as found in most 



