Family Ostraciidae 



Comparative diagnosis (contrast with that of the 

 Aracanidae). — Supraorbital region of the skull rela- 

 tively weak, the frontal extremely thin in this region and 

 tightly held to the undersurface of the carapace; frontal 

 without a long forward extension anterior to the orbit, 

 ending anteriorly over or only slightly in front of the 

 prefrontal and not overlying the ethmoid; supraoccipital 

 crest absent; epiotic little, if any, prolonged postero- 

 laterally, scarcely if at all beyond the level of the base of 

 the skull; prootic shelf without a recurved wing; 

 myodome either small and shallow or essentially absent; 

 usually three pharyngobranchials, occasionally only two, 

 the first a toothless suspensory element and sometimes 

 absent, the second with a series of small to minute teeth, 

 and the third either toothless or with minute rudi- 

 mentary teeth; branchiostegals 2 -I- 4; ethmoid a more or 

 less rounded shaft posteriorly and much expanded 

 laterally in the anterior one-third or more of its length; 

 pterosphenoid and parasphenoid with only a very limited 

 region of suturing in the interorbital septum; para- 

 sphenoid much expanded laterally throughout its length 

 anterior to its region of suturing with the anteromedial 

 edges of the prootic shelves, forming a complete hard 

 palate over the roof of the oral cavity; posterodorsal 

 region of coracoid without a posterior prong; four or five 

 vertebrae, represented by both neural arch and centrum 

 material, at the front of the vertebral column variously 

 fused and sutured to one another and to the exoccipitals 

 and basioccipital, the fusion region with a prominent 

 ventral process below the level of the centra; vertebrae 

 immediately following the fusion region with relatively 

 short neural spines and with centra of about normal 

 length without transverse processes; the centra of two or 

 more of the vertebrae immediately preceding the caudal 

 plate much compressed anteroposteriorly; haemal arch 

 and spine of the penultimate vertebra relatively small 

 and either autogenous or fused to the centrum, in which 

 latter case it may be rudimentary; caudal fin rays, i, 8, i; 

 postcleithrum of moderate size, formed of one or two 

 pieces, and not extending posteriorly much beyond the 

 level of the posterior edge of the pectoral girdle; carina 

 (supraneural) relatively short and either without a ven- 

 tral flange or with only a weak shallow one, not extending 

 anteriorly as far as the level of the anteroventral end of 

 the first dorsal fin basal pterygiophore and not in contact 

 with any of the neural spines of the predorsal vertebrae; 



haemal spines poorly developed and absent on many of 

 the abdominal and caudal vertebrae, except for the 

 heavy haemal spine(s) which supports by close apposition 

 and sometimes interdigitation the last anal fin basal 

 pterygiophore, the other anal fin basal pterygiophores 

 that lie in the midline of the body also making relatively 

 close contact along their distal ends with the vertebral 

 column; first anal fin basal pterygiophore expanded 

 anterolaterally at its distal end into wings supporting the 

 carapace; haemal canal not entirely straight, diverted 

 under the centra of the more posterior abdominal 

 vertebrae (usually between the seventh abdominal to 

 first caudal vertebrae) either to the left or to the right of 

 the midline, or alternatively to the left and right, and 

 relatively poorly enclosed under most vertebrae by weak- 

 ly developed haemal arches and spines; most of the 

 vertebrae posterior to the anteriormost four or five fused 

 vertebrae and anterior to the postanal vertebrae sutured 

 to one another (suturing between at least the fifth and 

 sixth abdominal vertebrae to the third and fourth caudal 

 vertebrae); uppermost pectoral fin ray short, composed 

 of a single piece without cross-striations and bearing a 

 foramen representing the region of otherwise complete 

 fusion between the original halves of the ray; body (ex- 

 clusive of vertical carapace spines) relatively less deep, 

 the distance between the distal ends of the first dorsal 

 and anal fin basal pterygiophores being contained more 

 than 3 times in SL, and the distance between the top of 

 the rear of the cranium and the ventralmost edge of the 

 pectoral girdle being contained about 2.3 to 2.5 times in 

 SL; carapace closed behind the anal fin and, with the ex- 

 ception of one species, behind the dorsal fin as well; 

 carapace never with a ventral keel; caudal peduncle 

 usually without scale plates isolated from the carapace 

 proper. 



Detailed description o( Acanthostracion quadricor- 



Material examined: — Thirteen cleared and stained 

 specimens, 8.2-350 mm; three dry skeletons, 130-163 mm. 



Occipital Region. 



Basioccipital. — A short column, expanded antero- 

 laterally; cartilage filled along its anterior and dorsal 

 edges; articulates by interdigitation dorsally with the 

 exoccipitals, anterolaterally with the prootics and 

 anteriorly with the overlying posterior end of the para- 



Figure 148. — Acanthostracion quadricornis: 



upper left, nasal region as seen externally 



(olfactory epithelium relatively smooth in 



this and all other species of ostraciids); 



lower left, outline of cross section of middle 



of body; pattern of scale plates shown 



only behind pectoral fin. 



