basibranchiaU 

 I rT~_3 — hypobranchials 



pharyngobranchials 



mterhyal "^^ 



^1 ,/^ ^ dorsal hypohyal 



epihyal U ^^ 



anchiostegal rays 



spinules of the individual scale plates, including the 

 variously enlarged central spinule, better developed than 

 in adults, i.e., the plates in the young are more highly 

 sculptured and ornamented than in adults. 



Aracanids generally have between 10 and 13 dorsal and 

 anal fin rays, with Capropygia and Caprichthys tending 

 to have closer to 13 dorsal and 12 anal and the other 

 genera tending to have closer to 10 or 11 in these fins, the 

 anal with the same number, or one less, than the dorsal. 

 All of the species tend to have either 10 or 11 pectoral fin 

 rays in addition to the small uppermost ray. 



There are usually 8 to 10 teeth in the upper jaw and 8 

 in the lower. The numbers of teeth found in the jaws of 

 the specimens examined (including alcohol preserved 

 material) are as follows, with the total in the upper jaw 

 followed by that of the lower jaw: Strophiurichthys 

 robustus, 9 and 8 in four specimens, 8 and 8 in one, 10 

 and 7 in one; S. inermis, 10 and 8 in one; Kentrocapros 

 aculeatus, 8 and 8 in one, 7 and 8 in one; Aracana aurita, 

 8 and 8 in one; A. ornata, 8 and 8 in two; Caprichthys 

 gymnura, 10 and 8 in two; Capropygia unistriata, 10 

 and 8 in two. 



In most osteological characteristics the aracanids are 

 remarkably similar, closely following the same general 

 plan in genus after genus. 



In Capropygia and Caprichthys, with relatively high 

 numbers of dorsal and anal fin rays, there are usually 12 

 dorsal fin basal pterygiophores and 11 anal fin basal 

 pterygiophores, while in the other genera these range in 

 number from 8 to 10. There are always seven predorsal 

 vertebrae, the more numerous rays and basal pterygio- 

 phores in Capropygia and Caprichthys being accommo- 

 dated toward the rear of the fin; e.g., the last pterygio- 

 phore of the dorsal fin in these two genera being placed 

 between the neural spines of the 13th and 14th verte- 

 brae, while in the other genera it is placed between the 

 12th and 13th. 



The branchiostegal rays are usually 2-1-4, except that 

 the single specimen of Caprichthys gymnura examined 

 had 2 -I- 4 on one side and 1 -(- 4 on the other, and that of 

 the two species of Aracana examined, the single speci- 

 men of A. aurita had 1 -(- 4 on both sides, while of the two 

 specimens of A. ornata examined one had 1 -I- 4 on both 

 sides and the other had 1 -(- 4 on one side and 2 -I- 3 on the 

 other. It would appear that in Aracana the branchios- 

 tegals are usually reduced to five, while the normal sit- 

 uation in Caprichthys awaits the examination of further 

 specimens, as it does also in Anoplocapros, no species 

 of which have been examined internally for this work. 



In Kentrocapros, Aracana, and Strophiurichthys the 

 second pharyngobranchial bears minute teeth, while in 

 Caprichthys and Capropygia it is entirely toothless. The 

 number of large teeth respectively on the third and 

 fourth pharyngobranchials are as follows for single speci- 

 mens of each of the species closely examined for this fea- 

 ture: Strophiurichthys robustus 6 and 6 (plus a few 

 smaller teeth on the third element in addition to the larg- 

 er ones); Aracana ornata 6 and 3; Aracana aurita 4 and 2; 

 Kentrocapros aculeatus 4 and 3; Caprichthys gymnura 3 

 and 2; Capropygia unistriata 3 and 2. Thus, Strophi- 

 urichthys has the best developed pharyngobranchial 

 dentition and Caprichthys and Capropygia the least, 

 with Aracana and Kentrocapros more or less interme- 

 diate. 



The ventral flange of the carina or supraneural is 

 deeper for a greater proportion of its length in the high 

 crested Strophiurichthys, Capropygia, and Caprichthys 

 than it is in the relatively flat-backed Kentrocapros and 

 Aracana. 



In Kentrocapros the autogenous haemal spine of the 

 penultimate vertebra is smaller than in the other genera. 

 In Kentrocapros, Aracana, and Strophiurichthys the 

 haemal canal enters the fused centrum-epural-hypural- 

 parhypural plate at the end of the vertebral column and 

 exits shortly behind at a prominent foramen low on the 

 plate, the foramen marking the region of fusion between 

 what would be the parhypural and lowermost hypural in 

 more generalized forms. In Capropygia and Caprichthys 

 this foramen is either absent or minute (Tyler 1970b: 18) 

 and the haemal canal which pierces the front edge of the 

 plate either stops within the plate or has only a minute 

 foramen that could not be detected in either of the single 

 specimens examined of the two species involved. 



In one of the species of Aracana, A. ornata, the snout 

 becomes convex and laterally expanded in adults, this 



