ASPIDORHYNCHUS. 



95 



Family ASPIDORHYNCHIDJE. 



Genus ASPIDORHYNCHUS, Agassiz. 



Aspidorhynchus, L. Agassiz, Poiss. Foss., vol. ii, pt. i, 1833, p. 14. 



Generic Characters. — Rostrum slender, much produced in advance of mandibular 

 symphysis ; circumorbital plates very small, postorbitals large ; teeth irregular in 

 size, largest on the premaxilla, palatine, and presymphysial bone, reduced to a fine 

 granulation on the inner face of the ectopterygoid ; branchiostegal rays short and 

 broad, and gular plate apparently absent. Vertebral centra in form of rings. 

 Fulcra wanting on paired fins, minute on median fins. Pelvic fins situated at 

 about the middle of the trunk ; dorsal and anal fins short-based, triangular, remote 



Fi«. 32. — Aspidorhynchus acutirostris (BlainviUe) ; restoration, about one-seventh nat. size. — Lower 

 Kimmeridgian (Lithographic Stone) ; Bavaria, br., branchiostegal rays ; cl., clavicle ; co. , circumorbitals ; 

 d., dentary ; /»•., frontal ; mx., maxilla ; n., narial opening ; op., operculum ; orb., orbit ; pmx., premaxilla ; 

 pop., preoperculum ; ps., presymphysial; pt., post-temporal; scl., supraclavicle ; smar., supramaxilla ; 

 so., postorbitals ; s.op., suboperculum ; st., supratemporal. 



and opposed ; caudal fin symmetrically forked. Scales robust, smooth or rugose ; in 

 two or three deepened series on the flank of the abdominal region, and the foremost 

 scales of the series traversed by the lateral line not deeper than the series below. 



Type Species. — Aspidorhynchus acutirostris (L. Agassiz, Poiss. Foss., vol. ii, 

 1833-44, pt. i, p. 14, pt. ii, p. 136, pi. xlvi; Esox acutirostris, H. D. de Blainville, 

 Nouv. Diet. d'Hist. Nat., vol. xxvii, 1818, p. 332), from the Lithographic Stone 

 (Lower Kimmeridgian) of Bavaria (Text-fig. 32). 



Remarks. — Reis 1 supposed that Aspidorhynchus was distinguished from the 

 closely related and partly contemporaneous genus Belonostomus, by the intercala- 

 tion of a supplementary triangular cheek-plate between its upper postorbital and 

 the preoperculum. This determination was adopted both by Zittel 2 and the 

 present writer, 3 but it is now clear that the appearance of such a separate plate is 



1 O. M. Reis, ' Ueber Belonostomus, Aspidorhynchus, und ilire Beziebungen zum lebeuclen L&pi- 

 dosteus,' Sitzungsb. k. bayer. Akad. Wiss., lnath.-phys. Cl., vol. xvii (1887), p. 173, pi. ii, fig. 7. 



2 K. A. von Zittel, Haudbueli der Palaeontologie, vol. iii (1887), p. 220, fig. 233. 



3 A. S. Woodward, Catal. Foss. Fishes, Brit. Mus., pt. iii (1895), p. 418, text-fig. 42. 



