GREGORY: FISH SKULLS 



149 



tained in the squamosal and prootic bones in many clupeids examined by Ridewood (1904a, 

 p. 62); (3) according to the same authority, in many clupeids there is an aperture, the 

 "temporal foramen" in the side of the cranium, bounded by the parietal and frontal bones. 

 "This in life is occupied by a fatty mass and in the dried skull leads directly from the 

 posterior temporal groove to the cavum cranii (1904a, p. 61); (4) a short distance behind 

 this is a lateral depression, the "pre-epiotic fossa," situated immediately in front of the 

 epiotic bone and bounded by the parietal, squamosal and epiotic. "The bottom of the 

 depression is composed of cartilage in Dussumieria and in Clupea harengus. . . ." These 

 details are of importance in the problem of the relationships of the Clupeidse with other 

 isospondyl families. 



Thus the skulls of the Clupeidse afford numerous examples of what might be called a 

 general principle of the morphology of the vertebrate skeleton, namely, that "the holes are 

 more important than the bones"; that is, the form and position of the bony tracts are 

 largely determined by the form and position of the sensory vesicles, blood-vessels, nerves, 

 muscles, etc.; the strengthening ridges and eminences appear between and around the 

 openings caused by the presence of the various parts mentioned above. 



Frost (1925a, p. 156) concludes that the otoliths of the Clupeoidea (from which he 

 excludes the Salmonoidea) appear to divide themselves into three groups which he names 

 the "Elopine," the "Clupeid" and the "Engrauline" types. 



Ctenothrissa radians 



Fig. 42. Ctenothrissa radians. After Smith Woodward. 



Ctenothrissa. — The Upper Cretaceous genus Ctenothrissa (Fig. 42), which is the type 

 of a family referred to the clupeoid division of the Isospondyli, is thus referred to by Smith 

 Woodward (1901, pp. vii, viii): "... Most of the Cretaceous forms are typical Clupeidae, 

 and they have scarcely changed during subsequent epochs. A few, however, discovered 

 only in Cretaceous rocks, are of special interest as exhibiting the precocious development 



