OCR Text |
Show 1904.] OSTEOLOGY OP CLUPEOTD FISHES. 493 over ; also in that the bullae in the squamosal and pro-otic bones present in other Clupeoid fishes for the lodgment of cfecal diverticula of the swim-bladder are wanting, as also are the auditory fenestra, the pre-epiotic fossa , and the temporal foramen also in the fact that the parasphenoid is not produced into a pair of posteriorly directed wings. On the other hand, such features as the reduction in the size of the mouth 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 supports neither the hypothesis of a natural affinity between Chanos and the Albulidfe, nor that which would associate Chanos with the Clupeidse; and the same may be said of the absence of teeth, the reduction in the number of branchiostegal rays, and the absence of surmaxilke. The closure of the posterior outlet of the eye-muscle canal is a mark of specialisation, and in this respect also Chanos differs from both the Albulidse and the Clupeidae (except Coilia). The absence of a subtemporal fossa, which is present in the Elopidse and Albulidse, but absent from the Clupeoid fishes, is an argument against Woodward's view; and again, the parietals meet one another in Albula, whereas in Chanos they are in reality separated by the supraoccipital, although a secondary union maybe brought about by means of the commissural sensory-canal bones which fuse with the parietals. Abbreviations employed in the Text-figures. bo, basioccipital. hr, branchiostegal rays. hs, basisphenoid. eh, ceratobranchial. cli, ceratohyal. cor, circumorbital bones. ct, cartilage. d, dentary. eh, epibranchial. ecp, ectopterygoid. eh, epihyal. af, auditory fenestra. al, alisphenoid. an, angular. ar, articular. bb, dentigerous plate covering the basibranchials. pef, pre-epiotic fossa. pi, palatine. pm, premaxilla. mx, maxilla. n, nasal. op, opisthotic. ope, opercular. or, orbitosphenoid. p, parietal. ph, pharyngobranchial. p o f postfrontal. pop, preopercular. p r f prefrontal. enp, entopterygoid. eo, exoccipital. ep, epiotic. frontal. git, glossohyal. hl>, hypobranchial. Iili, hypoliyal. hw, hyomandibular. ih, interhyal. iop, interopercular. me, mesethmoid. pro, pro-otic. ps, parasphenoid. pt, post-temporal. p tf posterior temporal fossa. q, quadrate. sar, sesamoid articular. sm, surmaxilla. soc, supraoccipital. sop, subopercular. sp, spicular bone. sq, squamosal. st, supratemporal. sy, symplectic. tf, temporal foramen. v, vomer. mpt, metapterygoid. |