Fi({ure laO.—Acanthostracion quadricornis: 

 lateral view of head, composite based on 

 several specimens, 58.2-350 mm SL, 

 Gulf of Mexico and Caribbean. 



pterosphenoid 



frontal 



prefrontal 



maxillary 

 premaxillaryXp"'*"'"* 



dentary 



articular 

 anguia 



quadrate 

 -interoperculom 

 ectopterygoid 



parosphenoid 



cartilage ' 



ethmoid \ V#f^^ 



vomer 



supraoccipital 



sphenotic 



symplectic 



basioccipital 



prootic \ parasphenoid 



metapterygoid , operculum 



■^ preoperculum \ i» i 



"^^^'y^J^ suboperculum hyomandlbular PO^«emporal 



essentially being absent. Two other genera are in various 

 ways intermediate between the two extremes of carapace 

 shape. In Lactoria the carapace is basically pentagonal, 

 with the distance between the ventrolateral ridges much 

 greater than that between the dorsolateral ridges, but 

 with only a low dorsal ridge, extended in two species (for- 

 nasinii and diaphana) into a prominent spine. In 

 Rhynchostracion the carapace in one species 

 (rhinorhynchus) is as rectangular as in Ostracion, while 

 in the other species (nasus) there is a prominent and 

 relatively high dorsal ridge so that the carapace is pen- 

 tagonal. In the pentagonal carapace of R. nasus the dis- 

 tance between the ventrolateral ridges is only very slight- 

 ly greater than that between the dorsolateral ridges and 

 this shape may be most closely related to the rec- 

 tangular form, while the pentagonal carapace of Lac- 

 toria, with the distance between the ventrolateral ridges 

 much greater than that between the dorsolateral ridges, 

 may be most closely related to the triangular form. 



Isolated scale plates on the caudal peduncle behind 

 the carapace are found only in Acanthostracion quad- 

 ricornis (commonly) and in A. polygonius (rarely, see 

 Tyler 1965a:8), in addition, of course, to the single large 

 plate found in Lactophrys trigonus, discussed above. 



In the only known fossil specimen of ostraciid, Eolac- 

 toria sorbinii from the Eocene of Monte Bolca, Italy, it is 

 impossible to say with assurity whether the carapace was 

 triangular, pentangular, or rectangular. However, there 

 is a slight indication (Tyler 1973a: 108) that the scale 

 plates along the region that would be the dorsolateral 

 ridge had larger central tubercules or spines than the sur- 

 rounding plates, suggesting that the dorsolateral ridge 



was prominent and that there was a dorsal crest, the 

 carapace perhaps being pentangular as in the Recent 

 Lactoria and Rhynchostracion rhinorhynchus. 



Spiny processes are present on the carapace except in 

 Ostracion, Rhynchostracion, and Rhinesomus triqueter. 

 In Acanthostracion, Lactoria, and the Eocene Eolac- 

 toria there are paired preorbital and postanal spines, 

 with Eolactoria having in addition an unpaired an- 

 teriorly directed spine between the eyes and Lactoria 

 having a well-developed spine on the dorsal ridge in some 

 species. In Lactophrys and Rhinesomus bicaudalis there 

 are postanal spines, while in Tetrosomus there are three 

 to five spines along the ventrolateral ridge, a supraor- 

 bital spine and one or two spines along the dorsal ridge. 



In general, the carapace of ostraciids is slightly more 

 fully consolidated than in aracanids, the only region with 

 much flexibility and unsutured scale plates being the 

 cheek, whereas in aracanids many of the scale plates 

 around the mouth and along the ventral region and 

 around the anus are often unsutured and slightly flexi- 

 ble. 



The number of teeth is slightly variable in ostraciids, 

 which tend to have a few more teeth in the jaws, es- 

 pecially the upper, than in aracanids. Most ostraciids 

 have 10 to 12 teeth in the upper jaw and 8 to 10 in the 

 lower jaw. There is only a slight tendency for an increase 

 in the number of teeth with increasing specimen size, ex- 

 cept in Lactoria diaphana, a relatively small species 

 which at sizes below about 30 mm tends to have 10 to 12 

 teeth in the upper jaw and 6 to 7 in the lower jaw, but at 

 larger sizes to have about 13 to 16 in the upper and 7 to 9 

 in the lower. The numbers of teeth in the upper and lower 



222 



