110 TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



The presence of large paired gular plates and the general appearance of the skull are 

 perhaps the most striking of the resemblances to the Palseozoic crossopterygians, but this 

 is attributed by Goodrich (1928) to convergence, since he regards the paired gulars of 

 Polypterus, which are derived from the median gular fold, as homologous not with the 

 similar appearing plates of true Crossopterygii, but with "the two anterior lateral gulars, 

 which are already becoming much enlarged in many Palaeoniscids." 



Goodrich has pointed out also that in all the more fundamental features of the scales, 

 dermal plates, skull morphology and even in the paired fins and girdles, Polypterus appears 

 to be allied with the Actinopterygii rather than with the true Crossopterygii, while especially 

 strong evidence in the same direction is found in the morphology of the auditory labyrinth, 

 pyloric caeca, urinogenital organs and brain. 



Goodrich regards the Polypterini as being related more or less closely to the palaeonis- 

 cids; Stensio (1921, p. 135) concludes that his account of the morphology of Dictyonosteus 

 and other coelacanthids "ought to show that neither the Coelacanthids nor the Rhipidistids 

 are so closely related to the Polypterids as has been believed previously. The Polypterids 

 represent rather, as Goodrich (1909, pp. 298-300) has pointed out, a type that is more closely 

 allied to the Actinopterygii, although in my opinion they cannot be grouped with these 

 either." In any case, Polypterus is of special interest since it is undoubtedly a specialized 

 descendant of a very ancient line and because it shows what has happened to certain skull 

 elements after divergence from the primitive palaeozoic ganoids. 



Among the archaic ganoidean characters of the Polypterus skull may be mentioned the 

 following: (1) the retention of a heavy ganoid armor, histologically close to that of the oldest 

 actinopterygian ganoids; (2) the retention of a spiracular cleft on the upper table of the 

 skull; (3) the retention of large "parietal" bones (parieto-dermopterotics of Allis) on the 

 upper surface of the skull, meeting each other in a long median suture; (4) the presence of a 

 cheek-plate which is more or less homologous with the tetrapod squamosal and which is 

 closely appressed to or united with the preopercular, bearing the hyomandibular branch 

 of the lateral-line canal (Allis), as in palaeoniscids (Goodrich); (5) the retention of paired 

 prevomers; (6) the close relation of the ectopterygoids with the maxillae; (7) the retention 

 of the dentigerous premaxillae and maxillae in their primitive position as an immovable 

 rim bordering the dentigerous plates of the primary upper jaw; (8) the retention of large 

 prearticular ("splenial") plates on the mandible; (9) the retention of a well ossified orbito- 

 sphenoid part of the brain trough; (10) the generally primitive arrangement of the lateral-line 

 canals on the skull. 



Advancing specialization is indicated by: (1) the enlargement of the maxilla, which has 

 apparently invaded the territory of the suborbital series, driving out or absorbing all but 

 the lacrymal and establishing a wide contact with the enlarged cheek-plate; (2) the presence 

 of a series of small plates, the spiracular ossicles of Allis (1922, p. 205), which may possibly 

 have been derived by the backward growth and simultaneous fragmentation of the dermo- 

 sphenotic; (3) the loss of the branchiostegals and lateral row of gulars; (4) the development 

 of a cranial buckler covered by tough skin suggesting that of catfishes; (5) the union of the 

 pterotics with the parietals; (6) the union of the 'allsphenoids' with the orbitosphenoids into 

 a sphenethmoid. 



According to Allis (1922, p. 248) the maxillary of Polypterus "has been formed by the 

 fusion of two suborbital latero-sensory ossicles with a dental bone that quite certainly 



