1904.^ 



OSTEOLOGY OF CLUPEOTD FISHES. 



493 



over ; also in that the bulla? in the squamosal and pro-otic bones 

 present in other Clupeoid fishes for the lodgment of c?ecal 

 diverticula of the swim-bladder are wanting, as also are the 

 auditoiy fenestra, the pre-epiotic fossa, and the temporal foi'ainen 

 also in the fact that the pai-asphenoid is not produced into a pair 

 of posteriorly directed wings. On the other hand, such features 

 as the reduction in the size of the moutli are as likely to be due to 

 convergence as to genetic affinity. 



The absence from the skull of Chanos of the orbitosphenoid and 

 basisphenoid bones is a mark of degradation, and supjDorts neithei- 

 the liypothesis of a natural affinity between Chanos and the 

 Albulidfe, nor that which would associate Chanoswith. tiie Clupeidse ; 

 and the same may be said of the absence of teeth, the reduction in 

 the numbei- of branch iostegal I'ays, nnd the absence of surmaxilla?. 

 The closure of the posterior outlet of the eye-muscle canal is a 

 mark of specialisation, and in this I'espect also Chanos differs from 

 both the Albulidee and the Clupeida^ (except Coilia). The absence 

 of a subtem]3oral fossa,, which is present in the Elopida* aiid 

 Albiilida", Ijut iibsent from the Clupeoid fishes, is a,n argument 

 against Woodward's view ; and again, the parietals meet one 

 another in Albula, whereas in Chanos they a,re in reality separated 

 by the supraoccipital, although a secondary union may be brought 

 aliout by meaiis of the commissural sensory-canal bones which fuse 

 with tlie parietals, 



Ahhreviations employed in the Text-figures. 



