anterior to the first basal pterygiophore of the soft dorsal 

 fin four to eight, those posterior to the last basal pteryg- 

 iophores of both the soft dorsal and anal fins four to six; 

 neural and haemal arches of the last centrum poorly 

 developed and nearly always incomplete (complete in 

 Brachaluteres trossulus); the last centrum with a 

 horizontal crest for muscle attachment (reduced to a 

 prong in B. trossulus); uroneurals never present; an 

 upper free hypural occasionally absent; lateral flanges 

 on the soft dorsal and anal fin basal pterygiophores end- 

 ing distally in prominent hooklike lateral expansions, 

 except in Chaetoderma spinosissimus and Rudarius 

 minutus; the basal pterygiophores extending proximally 

 relatively closely to the neural and haemal arches 

 usually only anteriorly in the length of the series; all 

 of the dorsal, anal, and pectoral fin rays unbranched; 

 scales small, with thin basal plates and usually fine 

 spinulation, the basal plates either overlapping or well 

 separated but usually not regularly arranged; scales 

 above the pectoral fin base unmodified; most species 

 relatively small, adults usually being 2(X) mm or smaller, 

 except for some species of a few genera (e.g., Canther- 

 hines, Nauodon) that have larger adults and, especially, 

 Alutera. at least one species (monoceros) of which 

 reaches over 5(K) mm (Berry and Vogele 1961:66). 



Detailed description of Monacanthua ciliatua. 



Material examined.— Twelve cleared and stained 

 specimens, 38.3-119 mm. 



SKULL. 



Occipital Region. 



Basioccipital. — A short column, expanded antero- 

 dorsally; cartilage filled at its anterior and anterodorsal 

 edges; articulates by interdigitation dorsally with the 

 exoccipitals, anteroventrally with the prootics, and 

 anteromedially with the overlying posterior end of the 

 parasphenoid. The rim of the round concave posterior 

 end of the basioccipital articulates by fibrous tissue with 



the concave anterior face of the centrum of the first 

 vertebra. The ventromedial surface of the basioccipital is 

 deeply concave throughout its length. This concave 

 channel is mostly hidden from view by the overlying 

 parasphenoid, but the channel opens to the exterior pos- 

 teriorly at the base of the posterior bifurcation of the 

 parasphenoid. Anteriorly the channel opens into the 

 myodome where the anterior end of the basioccipital 

 forms the posterolateral and posterodorsal walls of the 

 myodome. 



Exoccipital. — Cartilage filled along most of its ven- 

 tral, anterior, and dorsal edges; articulates through car- 

 tilage and slight interdigitation dorsally with the epiotic, 

 laterally through cartilage and interdigitation with the 

 pterotic, and ventromedially mainly through inter- 

 digitation with the basioccipital. Posteriorly the exoc- 

 cipitals form the lateral and ventral walls of the foramen 

 magnum, while dorsally the foramen is closed by the 

 epiotics. The posterior surface of the exoccipitals is 

 firmly attached by fibrous tissue and interdigitation with 

 the anterior surface of the bifid neural spine of the first 

 vertebra. A short posterior process from the postero- 

 medial portion of the exoccipital overlies the upper an- 

 terior region of the centrum of the first vertebra, this pos- 

 terior extention representing the modified exoccipital 

 condyle. 



Supraoccipital. — Widest posteriorly, where its 

 relatively flat dorsal surface is mostly obscured from ex- 

 ternal view by the large basal pterygiophore of the spiny 

 dorsal fin, but with a long forward extension above the 

 orbit with a vertical crest intervening between the fron- 

 tals and the anterior third of the basal pterygiophore; 

 cartilage filled along all of the edges of its posterior flat- 

 tened surface; articulates dorsally by interdigitation with 

 the basal pterygiophore of the spiny dorsal fin, pos- 

 teriorly through cartilage and interdigitation with the 

 epiotics, laterally and anteriorly, and ventrally on its an- 

 terior prolongation, through interdigitation with the 

 frontals, while the extreme anterior end of the anterior 

 extension reaches to the posterior end of the ethmoid in 

 large specimens. 



Figure 79.— Monacanthua ciliatus: 



upper left, nasal region as seen 



externally (far left) and the olfactory 



lamella as seen with the top of the nasal 



sac removed; middle left, scales from 



upper middle region of body, including 



two lateral line canal bearing scales: 



lower left, ventral view of encasing scales 



at end of pelvis (anterior to left). 



