Eolactoria is a representative of the line which gave rise 

 to Acanthostracion on the one hand and to Lactophrys = 

 Rhinesomus on the other, with the latter variously losing 

 the preorbital and postanal carapace spines, and that 

 another more specialized derivative of the Eolactoria to 

 Acanthostracion line gave rise to that of Lactoria and 

 Tetrosomus on the one hand and to that of Ostracion and 

 Rhynchostracion on the other, with the latter two genera 

 also losing the preorbital and postanal carapace spines. 

 Since all ostraciids have the ventral edge of the para- 

 sphenoid laterally expanded into a roof over the oral 

 cavity anterior to the level of the prefrontals, they can be 

 expected to have evolved from one of the two lines of 

 aracanids with a similar but less extensive expansion of 

 the ventral edge of the parasphenoid, either the Aracana 

 line with the expansion limited to a posterior region or 

 the Capropygia-Caprichthys line with the expansion 

 limited to an anterior region. However, it is impossible to 

 say with any confidence which one of these two lines was 

 more likely ancestral to the ostraciids (see discussion un- 

 der Aracanidae). 



SUBORDER TETRAODONTOIDEI 



(GYMNODONTES) 



Comparative diagnosis (contrast with that of the 

 Balistoidei). —Teeth either small rounded units or long 

 rodlike structures, but always nonprotruding and fully 

 incorporated into the matrix of the jaw bones, in one 

 family indistinguishably so, the otherwise discrete teeth 

 in molids no longer distinguishable from the bony 

 matrix, at least at 30 magnifications; dentaries and/or 

 premaxillaries often fused to their opposite members; 

 the medial articulation of the premaxillaries to one 

 another, if unfused, strengthened by alternating emar- 

 ginations and indentations, least developed in Triodon, 

 the most generalized member of the suborder; post- 

 temporal absent; urohyal absent, except in Triodon; 

 pelvis absent, except in Triodon; pelvic fin always ab- 

 sent; palatine relatively large and massive, always firmly 

 sutured or otherwise closely and immovably held to both 

 the ethmoid-vomerine region and the pterygoid arch; 

 myodome with a complete dorsal roof absent, except in 

 Triodon; prootic shelf under the orbit never present; 

 supracleithrum always placed distinctly obliquely to the 

 axis of the skull; scapular foramen incomplete, except in 

 Triodon; scapula without any special knob or crest for ar- 

 ticulation with the uppermost pectoral fin ray, except in 

 Triodon; distal pterygiophores of the soft dorsal and anal 

 fins always unossified; spiny dorsal fin absent, except 

 present as a rudiment placed far behind the skull in 

 Triodon; first I ^ranchiostegal ray modified, with a slight- 

 ly (Triodon) to enormously enlarged and inturned dorso- 

 medial edge, except unmodified in molids. 



Figure 180.— Body form in the only known Recent 

 species of Triodontidae: Triodon macroptenis. 



Infraorder Triodontoideo 



Comparative diagnosis (contrast with that of the 

 Tetraodontoideo), which is also that of its only con- 

 tained Superfamily, the Triodontoidea, and family, the 

 Triodontidae. — A rudimentary spiny dorsal fin of one or, 

 more usually, two small spines borne on two basal pte- 

 rygiophores present in most specimens of one of the 

 populations (Indonesia to Japan) of the single included 

 Recent species, the second basal pterygiophore succeed- 

 ed by two supraneural elements; ribs and epipleurals pre- 

 sent; caudal fin with 12 principal rays and numerous 

 procurrent rays; caudal fin deeply forked; caudal 

 skeleton with four separate hypurals, two uroneurals, 

 and a hypurapophysis; haemal spine of antipenultimate 

 vertebra autogenous; neural and haemal spines of penul- 

 timate vertebra long rounded shafts oriented highly 

 obliquely and directly supporting caudal fin rays; caudal 

 peduncle distinctly tapered to narrow transversely in- 

 dented regions above and below just in front of the 

 caudal fin, the least depth of the peduncle being about 

 3% SL and the least width at this region always greater 

 than the least depth; many of the caudal vertebrae with 

 large anterolateral processes from the region of the neural 

 arch and base of the neural spine; pelvis present; a huge 

 expansible dewlap of skin between the end of the pelvis 

 and anus, but no inflatability of the abdominal region; 

 cleithrum greatly elongate anteriorly, reaching forward 

 to between the lower jaw; basisphenoid a small rod plac- 

 ed far posteriorly in the interorbital septum and articu- 

 lated with the anterior edge of the dorsal roof of the 

 myodome; a large myodome present with a complete dor- 

 sal roof; a shallow channel present between the apposed 

 surfaces of the parasphenoid and basioccipital leading 

 into the myodome; scapular foramen complete, entirely 

 enclosed by the scapula; scapula with a distinct knob for 

 articulation with uppermost pectoral fin ray; four ac- 

 tinosts, none of which are sutured to one another or to the 

 scapula or coracoid; urohyal present; four pharyngo- 

 branchials present; fifth ceratobranchial well-covered 

 with prominent teeth; dentaries and premaxillaries 

 totaling three separate pieces; premaxillaries articu- 

 lated to one another by interdigitation or by only minute 



243 



