136 Eastman — Dipnoan Affinities of Arthrodires. 



surmise that such were developed;* moreover, in Goccosteus 

 we are confronted with a denticulated symphysial margin the 

 significance of which has not been explained. Finally, it 

 should be noted that an approach to the Dinichthyid form of 

 mandible is made even amongst Ctenodipterines,f and some of 

 these also developed cutting- surfaces, as in Sagenodus perten- 

 uis, for instance. 



Dentition of Mylostoma and Neoceratodm compared. — Our 

 knowledge of Mylostoma received important additions a few- 

 years ago, as the result of Dr. Bashford Dean's investigation 

 of the type species, M. variabile.% In the light, however, of 



Fig. 1. — Upper dentition of Mylostoma variabile Newb., from the Cleve- 

 land shale of Sheffield, Ohio, x %. 



freshly discovered material, it is clear that this author was not 

 entirely successful in determining the relations of the palato- 

 pterygoid plates in the unique specimen studied by him. 

 That their true arrangement is depicted in the accompanying 

 text-figure 1, can be proved in several ways, as follows : First, 

 in no other position is there snch accurate fit between upper 

 and lower dental plates when the jaws are closed. Secondly, 

 this reconstruction is in harmony with embryological evidence. 

 And thirdly, it is identical with the arrangement recently 



* Dean, B., Fishes, Living and Fossil, p. 133. (New York, 1895.) 

 f Atthey, T., On Ctenodus obliquus, etc., Ann. Mag. Nat. Hist. ser. 4, vol. 

 xv (1875). p. 309, pi. xix, fig. 2. By Sniith Woodward this species is consid- 

 ered identical with Sagenodus inozqualis Owen. 



| Dean, B., Pateontological Notes : On the Characters of Mylostoma New- 

 berry, Mern. N. Y. Acad. Sci., vol. ii (1901), pp. 101-109. 



