haemal spine on the antipenultimate vertebra; 5) the 

 procurrent caudal fin rays and at least one of the prin- 

 cipal rays (from the upper lobe of the fin); 6) a complete 

 dorsal roof to the myodome and the channel leading into 

 it posteriorly; 7) the knob on the scapula for articulation 

 with the uppermost pectoral fin ray, and the complete 

 scapular foramen; 8) urohyal; 9) one of the pharyngo- 

 branchials and well-developed teeth on the fifth cerato- 

 branchial; 10) the deep olfactory sac and normal olfac- 

 tory rosette; 11) four actinosts, none of which are sutured 

 to one another or to the scapula or coracoid. 



Triodon, as represented by the single Recent species 

 upon which our entire knowledge of the family is based 

 except for the fossil jaw fragments possibly related to it, 

 has certain features found in neither the triacanthodids 

 nor in other gymnodonts. These undoubtedly are 

 specializations which were acquired by Triodon after its 

 ancestral stock had given rise to the lines leading to the 

 molids on the one hand and to the tetraodontids and 

 diodontids on the other hand. These specialized features 

 of Triodon are: 1) the long caudal peduncle tapering to 

 a transversely indented region just in front of the base of 

 the deeply forked caudal fin; 2) the prominent antero- 

 lateral processes from the neural arch region of many of 

 the caudal vertebrae and the long rodlike neural and 

 haemal spines of the penultimate vertebrae, all as- 

 sociated with the musculature and support of the caudal 

 peduncle and caudal fin used for apparently sustained 

 rapid swimming; 3) the rotatability of the pelvis and the 

 expansible dewlap of skin between the end of the pelvis 

 and the anus; 4) the great anterior elongation of the 

 cleithrum; 5) the small sphenotic entirely confined to the 

 rear of the orbit; 6) the articulation of the first branchi- 

 ostegal ray on the ventrolateral surface of the cerato- 

 hyal; 7) the short posterior shaft of the interoperculum 

 behind the level of the epihyal; 8) the posteroventrally 

 prolonged shaft of the pterotic articulating broadly with 

 the hyomandibular; and 9) the exoccipital in contact 

 with the frontal and excluding the epiotics from contact 

 with the supraoccipital. 



Since neither the triacanthodids nor any of the other 

 gymnodonts possess anything similar to these specializa- 

 tions of Triodon, the ancestral line leading to the Recent 

 Triodon can be expected to have had more triacantho- 

 didlike conditions in these features and that they 

 remained relatively generalized in them until after the 

 other gymnodont linages split off from the early Triodon- 

 like fishes. 



The ancestral line connecting the eoplectin tri- 

 acanthodids and the triodontids is hypothesized as hav- 

 ing given rise to the line leading to the great diversifica- 

 tion of the gymnodonts, this line diversifying in two basic 

 directions, one leading to the molids and one to the 

 tetraodontids and diodontids, at a pre-Recent Triodon 

 level of organization, i.e., at a level of organization that 

 retained all of the generalized features of Triodon but 

 that did not yet have the specialized features of the Re- 

 cent Triodon noted above, as well as with both the pre- 

 maxillaries and dentaries unfused and the first branchi- 

 ostegal ray entirely unmodified. 



The molid line of radiation from the pre-Recent 

 Triodon level of organization is represented by only a few 

 species, at least surviving today, which became vastly 

 modified for a slow swimming oceanic and mostly pelagic 

 existence and relatively huge size within a protective 

 wall of thickened skin, while retaining from its triodon- 

 tid ancestry several generalized features lost in the 

 tetraodontid-diodontid line of radiation. Molids have 

 retained: 1) the basisphenoid; 2) fourth gill and gill slit 

 between the fourth and fifth arches; 3) unmodified first 

 branchiostegal ray; 4) uninflatable gut; and 5) un- 

 sutured ceratohyal and epihyal. 



Moreover, the configuration of the bones of the snout 

 in molids is in many ways remarkably similar to that in 

 Triodon, far more so than is the case in the tetraodontid- 

 diodontid line. In Triodon and molids the ethmoid tends 

 to be a large squarish block of bone bordered on either 

 side by the large palatines and prefrontals, with the 

 palatine broadly held medially to the ethmoid, vomer 

 (unossified in Ranzania), parasphenoid and prefrontal. 

 The shape and size of the frontals in Triodon and molids 

 is also remarkably similar. An anteriorly directed prong 

 in the suboperculum, as found in Triodon and diodon- 

 tids, is retained in molids, even though the molid oper- 

 culum and suboperculum are greatly reduced in size. 



While these similarities between Triodon and molids 

 indicate the relationship between the two groups, molids 

 possess an array of specializations beyond the generaliz- 

 ed Triodon level of organization, many of which are cen- 

 tered around the aborted rear end of the body and the 

 support of the continuous dorsal, anal, and pseudo- 

 caudal fins. The major ways in which molids differ from 

 Triodon, other than those already mentioned above that 

 distinguish Triodon from all other gymnodonts, whether 

 they be the generalized triacanthodidlike features of 

 Triodon that are lost or the specialized features of 

 Triodon developed after the radiation of the other gym- 

 nodonts from a triodontid ancestral group, are: 1) the 

 apparently indistinguishable incorporation of the dental 

 material into the matrix of the jaws, along with the fu- 

 sion of the premaxillaries, even though well-developed 

 individual trituration teeth are retained in both the up- 

 per and lower jaws; 2) the loss of an ossified sesamoid ar- 

 ticular; 3) the great enlargement of the basisphenoid and 

 the complete loss of the dorsal roof of the myodome and 

 of the posterior opening into it; 4) the loss of teeth on the 

 fifth ceratobranchial and the development of gill rakers 

 along the front of the fifth ceratobranchial and along the 

 anterior edge of the first gill slit, even though only 

 Triodon and molids among the gymnodonts retain the 

 fourth gill, well-developed teeth on all three of the tooth- 

 ed pharyngobranchials, unsutured ceratohyal and 

 epihyal, the consistent presence of both dorsal and ven- 

 tral hypohyals and the interhyal, and a relatively un- 

 modified first branchiostegal ray; 5) the loss of the 

 pharyngobranchial of the first arch; 6) the loss of the first 

 or uppermost actinost; 7) the consolidation of the post- 

 cleithra into a single piece and the development of an an- 

 terior spur from it to the region of the actinosts; 8) the 

 development of a dome or posterior prolongation on the 



