9 2 Memoir Sears Foundation for Marine Research 



The Order Isospondyli, as defined under Characters of Living Isospondyli, cor- 

 responds to: the Order Isospondyli of Cope;^" the Suborder Isospondyli in part of 

 Woodward (5^: xxxvi; 5^: xvii); the Suborder Malacopterygii plus the Suborder 

 Haplomi in part of Boulenger (7); the Suborders Clupeiformes and Esociformes of 

 Goodrich {25: 386, 397); the Orders Isospondyli (excluding the Mormyriformes) and 

 Haplomi of Regan (jS: 77—78); the Orders Clupeiformes plus Galaxiiformes of Berg 

 {4: 216,254,256,417,436,437); the Order Isospondyli of Romer (^5: 581,584) 

 plus the Suborder Esocoidea, which he referred to the Order Mesichthyes of Hay 

 {20: 397); and the Order Clupeiformes of Bertin and Arambourg {18: 210). 



The members of the Order Isospondyli include some of the most generalized of 

 living bony fishes, and the fossil record for some of them reaches as far back in geo- 

 logic time as the Lower Cretaceous (p. 15). The Order is accepted here as a matter 

 of convenience, since the interrelationships of its included units still remain obscure. 



Suborders. The heterogeneous assemblage that is grouped together in Part 5 as the 

 Order Iniomi has been treated as a Suborder of the Isospondyli by some authors 

 (Schultz and Stern, ^7: 233 ; Bertin and Arambourg, 18: 2269) but as a separate Order 

 by Regan {38: 77-78; ^J: 314), Jordan {22: 153), Norman {30: 317), Berg {4: 242, 

 256, 429, 437 — as Scopeliformes), and Marshall (26: 305—336). In accord with pres- 

 ent-day tendencies based on evolutionary grounds, discussed below, the Iniomi are 

 here classed as a separate Order. 



In 1929 Regan {41: 313, 314) set the Iniomi apart from the Isospondyli as a 

 separate Order on the following grounds: 



I a. Maxillaries (typically) forming a part of upper border of mouth ; pectoral girdle 

 with mesocoracoid element in the great majority. Isospondyli. 



I b. Maxillaries not forming a part of upper border of mouth; pectoral girdle without 

 mesocoracoid element. Iniomi. 



Unfortunately, the separation between Iniomi and Isospondyli is not as clear-cut 

 as the foregoing implies. Thus the mesocoracoid is lacking: in some of the Argenti- 

 noidea (5J: 609, 612); in the Salangidae (Salmonoidea); in the Retropinnatidae, the 

 systematic relationships of which remain uncertain; in the Esocoidea (Part 4), the 

 Bathylaconoidea (55: 52), and the Aplochitonidae {40: 290), which have sometimes 

 been grouped with the Salmonoidea but which seem to deserve the rank of a separate 

 Suborder. Furthermore, the Iniomi share the withdrawal of the maxillary bone from 

 the upper border of the mouth with some fishes that are isospondylous in other respects : 

 i. e. the genus Albula (Albulidae), the Pterothrissidae (here rated as a separate family), 

 Nematalosa (44: 465, fig. 127, as "C/iaeloessus"), and the genus Chanos. 



Such members of the Order Isospondyli as are known to occur in the western 

 North Atlantic are distributed in Parts 3 and 4 among the Suborders Elopoidea, Clu- 



20. The systematic position of Cope's (ii: 454) Scyphophori (freshwater families Mormyridae — distinguished espe- 

 cially by the enormous cerebellum — and Gymnarchidae) remains controversial. 



