BONES FOEMING OPERCULAR SERIES OF FISHES 69 



ized offshoots of the typical Acanthopteri. In fact, it seems safe 

 to assert that none other of the known characters which separate 

 this series from the lower teleosts has been more conservatively 

 maintained throughout the entire group. This statement may 

 be emphasized by the naming of a few of the more aberrant types 

 which differ in some notable way^ — primitive, specialized, or 

 degenerate — from the group as a whole, yet which agree with 

 one another and with the more typical members of the series in 

 the essential characters of their branchiostegal apparatus: 

 Atherina, Stephanoberyx, Plectrypops, Cepola, Psettus, Toxotes, 

 Monacanthus, Lactophrys, Tetraodon, Diodon, Agonus, Cyclop- 

 terus, Cephalacanthus, Echeneis, Solea, Callionymus, Xiphidion, 

 Scytalina, Gobiesox, Coryphaenoides, Antennarius, Ogcocephalus, 

 etc. Broad union of the branchial membranes or their complete 

 separation, membranous or fleshy character of the branchiostegal 

 membranes, narrow lateral restriction or wide development of 

 the branchial aperture, and countless other modifications of these 

 higher teleosts occur — modifications affecting almost every part 

 and structure of the body, as well as the branchial membranes^ — 

 nevertheless, the essential characters of the branchiostegals 

 remain unaltered." 



The characteristically stout hyoid arch is strongly angulated'' 

 at some distance below and before the (typically) dentate suture 

 between the ceratohyal and the epihyal, the angle forming the 

 hinder border of a concavity in which the musculus geniohyoideus 

 is attached. The strong development of this muscle not only 

 modifies the form of the hyoid arch, but also modifies the structure 

 and attachment of the branchiostegal rays, as it also does, usually 



* Certain of the individual rays may become reduced or specialized : for 

 example, in Tetraodon the uppermost ray basally is an unossified ligament, 

 while the lowest ray (as in Diodon) is greatly expanded; in Holotrachys the third 

 to the seventh branchiostegals are strongly armed externally by rows of spinules; 

 in Polymixia the lower three rays are modified, according to Starks, into a 

 skeletal support for the barbel. 



^ The hyoid arch is also angulated, but in not quite the same way, in a few 

 of the soft -rayed types, notably in Brevoortia, Dorosoma, Notopterus, and Gono- 

 rhynchus. In most of the lower teleosts the hyoid arch is a thin plate, and the 

 suture between the epihyal and the ceratohyal is straight and often margined 

 with cartilage. 



