CLUPEIFORMES 397 



the Ctenothrissidae are placed in the Clupeiformes chiefly on account of 

 their osteology ; yet in the position of their pelvic fins and the spine- 

 like dorsal rays, they approach the Acanthopterygii, with which they are 

 possibly related. 



Ctenothrissa, A. S. W. (Fig. 388), and Aulolepis, Ag. ; Cretaceous, 

 Europe and Asia Minor. 



Sub-Group 2. 



In which the mesocoracoid arch is lost and a higher level 

 of general specialisation is reached, usually accompanied by the 

 closure of the pneumatic duct, the development of spines and 

 ctenoid scales, and the modification of the maxilla into a toothless 

 bone, separately articulated, and lying behind the premaxilla. 

 This last character has been independently developed in the 

 Cypriniformes and probably also in several of the following 

 sub-orders. Except in the Berycidae (Starks [421]) and Lampridi- 

 formes (Regan [344]), the orbitosphenoid is lost. Seven sub-orders 

 are included, some of which are merely provisional assemblages of 

 families, whose affinities are by no means clearly established. 

 Indeed, the origin of the Anguilliformes, for instance, is quite 

 unknown ; but, since the Acanthopterygii appear to be more 

 closely related to two of the sub-orders than to the others, we 

 can distinguish five divergent series which may be of some phylo- 

 genetic value. 



Series 1. 

 Sub-Order 1. ESOCIFORMES (Haplomi). 



This is a provisional sub-order containing some of the least 

 specialised forms of Sub-Group 2 (Starks [420]). They are with- 

 out true spines, and are usually physostomouS (with an open pneu- 

 matic duct). As a rule, the parietals are separated and the 

 orbitosphenoids absent. The pelvic fins are abdominal, and may 

 have numerous dermal rays ; the dorsal fin single, though occa- 

 sionally followed by an adipose fin. 



In general structure the Esociformes resemble the Clupeiformes, 

 the Cyprinodontids lead towards the Mugiliformes, while the 

 Scopelids and Stephanoberycids approach the Acanthopterygii 

 (Boulenger). Fossil forms are known from the Eocene upwards. 



TRIBE 1. 



The parietals meet, separating the frontals from the supraoccipital ; 

 the post-temporal is simple ; the neural arches and parapophyses generally 

 autogenous (Swinnerton). 



