Family Monacanthidae 



Comparative dia^osis (contrast with that of the 

 Balistidae). — The more or less incisorlike teeth relative- 

 ly more delicate, developed for nibbling, three outer and 

 two inner on each premaxillary, and three, occasionally 

 only two, in a single series on each dentary; pharyngo- 

 branchials consisting only of two uniserially toothed 

 elements; fifth ceratobranchial toothless but with a 

 series of gillrakers along its anterior edge (posterior edge 

 of last gill slit); usually two dorsal spines, sometimes 

 only one, the second spine, when present, not more than 

 about one-third the length of the first, and usually much 

 smaller, ending ventrally in delicate ventrolaterally 

 directed prongs from either side; dorsal fin spines sup- 

 ported by a single basal pterygiophore, without a supra- 

 neural strut; dorsal spines and at least most of the length 

 of the basal pterygiophore placed over the top of the 

 skull; no lateral foramen in the basal pterygiophore to ac- 

 commodate the venterolateral prongs of the second dor- 

 sal spine; at least the posterior region and usually all of 

 the supraoccipital a flat or slightly rounded thin plate 

 without a vertical crest and broadly overlain (only slight- 

 ly in Psilocephalus) by the first basal pterygiophore 

 above it, while in some genera an anterior prolongation of 

 the supraoccipital above the orbit bears a vertical crest 

 for articulation with the ventral edge of the vertical 

 platelike portion of the anterior region of the first basal 

 pter>-giophore; posterior region of the epiotic not ex- 

 panded dorsally, the medial edges of the two epiotics in 

 contact throughout their lengths, there being no large 

 foramen in the skull between the epiotics and the supra- 

 occipital; palatine more or less rodlike, never distinctly 

 T-shaped, but sometimes with a bulge or short process on 

 its ventral edge representing a rudiment of the long foot 

 of the T as found in balistids, usually connected by a long 

 ligament with the anterior edge of the ectoptergiod; ex- 

 occipital not meeting its opposite member in the midline 

 above the foramen magnum, only slightly if at all 



protruding medially beyond the medial edge of the bifid 

 neural spine of the first vertebra; prefrontal relatively 

 small and delicate, articulated by fibrous tissue mainly 

 with the frontal and sometimes, to a much lesser extent, 

 with the ethmoid, but never directly contacting the para- 

 sphenoid; parasphenoid moderately to much expanded 

 laterally just behind the orbit (except in the elongate 

 Psilocephalus), the medial edge of the pterotic on the 

 ventral surface of the skull broadly separated from its op- 

 posite member there by the basioccipital and para- 

 sphenoid; parasphenoid not expanded or only very 

 slightly expanded dorsally in front of the orbit, only 

 slightly if at all overlying the ethmoid and not con- 

 tacting the prefrontal; the laterally expanded dorsal 

 region of the ethmoid relatively narrow and thin, much 

 less wide than the depth of the ventral platelike portion 

 ventral platelike flange of the ethmoid thin and delicate 

 relatively deep, much deeper posteriorly than an 

 teriorly, and only slightly if at all overlain by the para 

 sphenoid; posttemporal (absent in Psilocephalus) held 

 more superficially and in a much less deep groove on the 

 lateral surface of the pterotic; medial edge of dentary al- 

 ways denticulate; prootic shelf less well developed (and 

 sometimes absent), not extending forward to the level of 

 the middle of the orbit, except in Psilocephalus in which 

 it reaches the front of the orbit; posterior edge of supra- 

 cleithrum relatively straight and not posteriorly ex- 

 panded; postcleithrum without a dorsal spur on its dor- 

 sal edge and no specialized tympanal region present; 

 postcleithrum always a single piece; branchiostegal rays 

 2 -(- 4, 1 -I- 4, or 1 -I- 3; pelvis with or without a dorsal lobe 

 posteriorly on its dorsal surface; encasing scales at the 

 posterior end of the pelvis in three or fewer segments, or 

 of indeterminate number or absent, when present either 

 flexible or fixed; a rudimentary pelvic fin element either 

 present or absent; vertebrae 19 (usually 7 -I- 12, sometimes 

 6 + 13) or more (7 or 8 -I- 13 to 23), up to 30; vertebrae 



Figure 78.— Range of diversity in 



body form in the Monacanthidae: 



A. Monacanthus ciliatus; 



B. Amansea acopas; 



C. Brachaluteres trossulus; 



D, Pnlocephalua barbatua. 



