68 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



rudimentary and not movable (fig. 5), absent in 

 specimens larger tlian 135 mm. S.L. Gill slit, 

 oblique at an angle of about 45° to horizontal 

 body axis in specimens larger than 40 mm. S.L. 

 (fig. 4). First dorsal spine, inserted over mid or 

 posterior part of eye (fig. 4). No deep groove 

 behind dorsal spines. Body depth, 27.6 to 46.5% 

 S.L. (table 12; fig. 35). Head length, 29.1 to 

 35.2% S.L. (table 13). Snout length, 23.8 to 

 28.7% S.L. (table 14). Eye diameter, 6.2 to 

 10.0% S.L. (table 15). Eye to dorsal spine 

 distance, 4.0 to 7.3% S.L. (table 16; fig. 34). 



Specimens examined. — 68 of 30.5 to 240 mm. 

 S.L., from Bermuda, from southern Massachusetts, 

 off the coast of the Carolinas, around the Florida 

 coast, in the Gulf of Mexico, and off Brazil (fig. 

 38). 



Color. — In live specimens taken off North 

 Carolina in September 1959, the scrawled mark- 

 ings and spots were bluish purple ; the background 

 color was a mottled olive brown that faded upon 

 preservation. The pigmentation of the markings 

 and spots remains dark on most specimens even 

 after prolonged preservation. 



Monacanthus Oken 1817 



We have examined two valid species of this 

 genus from the western North Atlantic, M. 

 tuckeri Bean 1906 and M. ciliatus (Mitchill) 1818. 



The two species of Monacanthus in the western 

 North Atlantic were recorded in a new subgenus, 

 Leprogaster, by Fraser-Brunner (1941: p. 184). 

 He distinguished it as an Atlantic subgenus 

 characterized by a shorter pelvic spine and a 

 smaller ventral flap than are present in the 

 Pacific subgenus Monacanthus. We found no 

 elongation of the upper caudal ray in the Atlantic 

 species as was depicted by Fraser-Brunner for his 

 new Pacific species, Monacanthus macrolepis 

 (1941: p. 190, fig. 4). 



Monacanthus tuckeri apparently is a smaller 

 species than M. ciliatus, both in not growing to so 

 large a size and in maturing at a smaller size. 

 Based on the specimens we examined it appears 

 to be the less abundant of the two along the 

 United States coast, but more equally common 

 with M. ciliatus in the Bahamas and Bermuda. 



In his revision of the Aluteridae Fraser-Brunner 

 (1941) recorded both Monacanthus and Stephano- 

 lepis as valid and distinct genera. Since then 



several workers have disagreed with this pro- 

 nouncement and have regarded Stephanolepis as 

 a s_\monym of Monacanthus. The probable reason 

 for this disagreement is the interpretation of scale 

 structure of the two nominal genera. We have 

 found the scale structure is subject to ontogenetic 

 change — not adequately accounted for by Fraser- 

 Brunner. Scales of various sizes of specimens of 

 Stephanolepis hispidus and Monacanthus ciliatus 

 are diagrammatically illustrated in figure 8. In 

 the structure and ontogeny of its scales, Stephano- 

 lepis setifer is essentially similar to S. hispidus, as 

 is Monacanthus tuckeri to M. ciliatus, except that 

 M. tuckeri is smaller at maturity than is AI. 

 ciliatus and exhibits changes in its scale structure 

 at smaller sizes. 



The scales of all four genera of filefish examined 

 during this study have one or more spines arising 

 perpendicularly from the scale base, the number of 

 spines increasing with growth or size of the fish. 

 Above the scale base the spines are usually curved 

 posteriad, and they may undergo certain modifica- 

 tions as secondary sexual characteristics, partic- 

 ularly in the region of the caudal peduncle. The 

 scales of Alutera and Amanses are similar to those 

 of Monacanthus. The scales of Monacanthus and 

 Stephanolepis are similar up to a size of about 20 

 mm. S.L., the scales of each having a single spine 

 (fig. 8). At sizes larger than 20 mm. S.L., the 

 spines of some of the scales of Stephanolepis have 

 become branched — this branching occurs well 

 above the scale base usually on the distal one- 

 fourth of the spine. Between 30 and 40 mm. S.L. 

 the spines of essentially all of the scales of Stepha- 

 nolepis have become branched. Two or more 

 closely joined spines are present on scales of 

 Stephanolepis of more than 100 mm. S.L., and eight 

 were present on the scales of a 150-mm. S.L. speci- 

 men — aU of these spines are branched. Con- 

 versely, the scale spines of Monacanthus never 

 branch — each spine arises individually from the 

 scale base. Two spines were found on a few scales 

 of a 41-mm. S.L. specimen of Monacanthus ciliatus, 

 three at 46.5 mm. S.L., and seven at 95 mm. S.L. 

 (fig. 8) . Some of the spines on larger specimens of 

 Monacanthus are jomed basally by a thin bony 

 partition. 



After analyzing these concrete differences in 

 scale structure in the two groups, as well as distinct 

 differences in secondary sexual characters, we 



