132 



TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



separating the antorbital from the lacrymal are precisely like other and certain sutures 

 near by. 



tabC'SCaleboneV 



deth 



Eugnathus 



Fig. 27. Eugnathus. After Smith Woodward. 



The beautiful figure of this skull published by A. S. Woodward gives a very accurate 

 record of the facts, especially as regards sutures. The postorbital plates, the beginnings 

 of which have been seen in the palaeoniscids, are very large but now few in number and 

 there is a much higher degree of differentiation between adjacent elements of the surface 

 pattern than was the case in the primitive semionotids. The operculars and branchiostegals 

 all obviously form part of a single opercular fold. They are all wider antero-posteriorly 

 than those of primitive palaeoniscids. They agree, however, with the semionotid type in 

 the important fact that the interopercular is in horizontal alignment with the subopercular, 

 thus lending weight to Tate Regan's suggestion that the interopercular represents a 

 separated extension of the antero-inferior corner of the subopercular. Both the sub- and 

 inter-opercular lie immediately dorsal to the long first branchiostegal. Examination of 

 this fine specimen of Eugnathus reveals a small transversely-extended bone lying above the 

 premaxillse and below the broad nasals, which seems to be the median ethmoid, as it corre- 

 sponds to a similar bone in Lepidosteus and Amia. The broad plates in front of the frontals 

 have the appearance of being homologous with the nasals of Amia and the teleosts and 

 possibly also with the paired postrostrals of palaeoniscoids (c/. p. 113). 



The hyomandibular of Eugnathus is directed at first gently backward and then for- 

 ward, essentially like those of the Semionotidae on the one hand and of the teleosts on the 

 other, and unlike the more sharply inclined suspensorium of the primitive palaeoniscids. 

 This contrast is related with the fact that in Eugnathus the snout is relatively elongate 

 and the eye far backward, while in the palaeoniscids the opposite conditions are found. 

 Also correlated with this difference is the profound contrast in the preopercular, which in 

 paljeonis'cids is large, inclined forward and spread over the upper part of the cheek, but 

 in the primitive amioids small, vertical, inclined slightly backward and limited to the 

 lower part of the cheek. The maxillae are now freed at their posterior end from the 



