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Show 1894.] SALMONOTD FISHES OF THE ENGLISH CHALK. 663 length. Further, it is known that the double supramaxilla is not quite constant in the Clupeoids, Elopines, and their allies. It may also be argued that, as Dr. Giinther admits to the Clupeidae living fishes with a gular plate (Ehps, Megahps), there is no reason for excluding from the Salmonidae any primitive fishes Avhich differ only from the living members of this family in the possession of such a plate. Nevertheless, so far as the present writer is aware, supramaxillaries of the form described above in Osmeroides and Aulolepis have not hitherto been observed in any Salmonoid, while they- are a A*ery common feature among Clupeoids and Elopines. The two Cretaceous genera under discussion may therefore be provisionally associated with the latter. The fishes named Osmeroides from the Chalk of Mount Lebanon may also be placed here, for they likewise exhibit a large gular plate ; and Elopopsis is already assigned to the same systematic position by common consent. Ehps and Megahps, indeed, have many more close allies in Cretaceous and early Tertiary strata than has hitherto been suspected, and the type they represent seems to have been dominant among the earliest Physostomi. EXPLANATION OF THE PLATES. PLATE XLII. Fig. 1. Osmeroides lewesiensis; fish from ventral aspect, two-thirds nat. size. a., base of anal fin; d., dentary; gu., gular plate; mx., maxilla; op., operculum ; pet., pectoral fins; ph., pelvic fins ; s.mx.z, posterior supramaxillary; s.op., suboperculum. [P. 7188.] 2. Ditto; hinder portion of cranial roof, upper aspect, jr., frontal; pa., parietal; s.t., supratemporal; sp.o., supraorbital; sq., squamosal. [4295.] 3. Ditto; side view of head. 3 a. Rostral region of same specimen, upper aspect, br., branchiostegal rays ; m.pt., metapterygoid ; d., dentary; ectp., ectopterygoid; eth., ethmoid ; fr., frontal; mx., maxilla; op., operculum; orb., orbit; p.op., preoperculum; pt.o., postorbital; qu., quadrate; s.mx. i, 2, supramaxdlaries; s.op. suboperculum. [4296.] 4. Ditto; right quadrate {qu.), metapterygoid (m.pt.), and symplectic (sym.), outer aspect. [P. 5680.] 5. Ditto; left maxilla (mx.) and supramaxillaries (s.mx. 1, 2), outer aspect. 5 a. Symphysis of mandible, oral aspect, showing attachment of teeth. [49891.] 6 Ditto- right mandibular ramus, outer aspect. ag., angular; d., dentary. [4296.] P L A T E XLIII. Fie 1 Elopopsis crassus ; lateral view of head, two-thirds nat. size. 1 a. Upper ' view of ethmoidal region. 1 b. Left premaxilla, outer aspect, 1 c. Left dentary, outer aspect, eth., ethmoid; fr., frontal; md., mandible • mx., maxilla; orb., orbit; p.op., preoperculum; pmx., premaxilla; pt.o., postorbital; s.mx., supramaxillary; s.o., suborbital rWillett Collection, Brighton Museum, no. 61.] 2 Aulolepis typus; imperfect fish, dorsal aspect 2a. Right mandibular ' ramus, ag., angular ; ar., articular; d., dentary; d.f, dorsal fin ;. fr., frontal; pa., parietal; sq., squamosal. [P. 5681.] 3. Ditto; right frontal, upper aspect. [P. 1854.] |
