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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



of a character which was never permanently acquired by fishes with so primitive a skull, 

 but soon became the common feature of the spiny-finned or acanthopterygian families. 

 These are the Ctenothrissidae, which have hitherto been mistaken for Berycoids because 

 they display the character in question, namely, the forward displacement of their pelvic 

 fins, which are situated more or less directly beneath the pectoral pair. The few undivided 

 rays in front of their fins, however, are always articulated distally and never form true 

 spines." Tate Regan (1907a, p. 642) also concludes that "the Beryciformes [the most 

 primitive of the spiny-finned groups] may have evolved directly from Malacopterygil, such 

 as the Cretaceous Ctenothrissa and Pseudoberyx, to which they bear considerable resem- 

 blance." 



Smith Woodward in his paper on "The Antiquity of the Deep Sea Fish Fauna" (1898; 

 also 1912, p. 254) has noted that many of the Cretaceous isospondyls find their nearest 

 relatives today in the deep-sea fauna, and that these modern relicts "probably migrated 

 to the ocean depths during the Tertiary period as the competition from newer types of 

 fishes has increased." Through the courtesy of Dr. William Beebe I have been enabled 

 to examine the skull structure of the principal types of deep-sea isospondyls. Our observa- 



pmK 



Opisthoproctus 



Fig. 43. Opisthoproctus. 

 Diagram of skull of specimen kindly loaned by Dr. William Beebe, who will publish a full description of this rare specimen 



