342 



LEPIDOSTEOIDEI 



The vertebral centra (Gegenbaur [154], Balfour and Parker 

 [30]) are quite exceptional among fishes for having a concave 

 posterior and a convex anterior face ; they are thus opisthocoelous 

 (Fig. 322). The skeleton of the paired fins resembles that of 

 Amia, though more reduced. 



The spiracle is closed, but a well -developed opercular gill 

 persists (hyomandibular posterior demibranch), Miiller [305]. The 

 pyloric caeca are numerous, and the median dorsal air-bladder is 



'" SO/). 



fir. 



FIG. 321. 



Lepidosteits ossens, L. A, oblique view of the skull from behind ; B, inner view of the right 

 opercular bones and upper jaw broken short in front ; C, inner view of the hind end of the 

 lower jaw ; D, lower portion of hyoid arch, belonging to B. an, angular ; or, articular ; ar.p, 

 articular process for rhetapterygoid ; bh, basihyal ; bo, basioccipital condyle ; In; branchiostegal ; 

 ch, ceratohyal ; d, dentary ; da, posterior splenial ; dp, palatine; eh, epihyal; ep, epiotic ; e.x, 

 lateral wing of basioccipital (fused neural arches) ; /, frontal ; h, hyomandibular,; hh, hypohyal ; 

 iop, interopercular ; mk, Meckel's cartilage ; ms, endopterygoid ; mt, metapterygoid ; op, 

 opercular ; opo, exoccipital (probably including opisthotic) ; p, parietal ; pa, parasphenoid ; pop, 

 preopercular ; pro, prootic ; pt, ectopterygoid ; pto, postfrontal ; q, quadrate ; *, symplectic ; 

 so., supra-angular ; sop, subopercular ; sp, splenial ; sq, pterotic ; st, supratemporal. 



lung-like with cellular walls (p. 224). The conus arteriosus is very 

 long, with very many rows of valves (Fig. 323). In the presence of 

 a closed ovisac, communicating only to the exterior by the oviducts, 

 Lepidosteus shows a remarkable resemblance to the Teleostei (Fig. 

 355, D, and p. 366). The genital ducts in both sexes open together 

 with the kidney ducts by a median pore. The cleavage of the 

 egg is meroblastic. The larva has preoral adhesive organs. 



Jn many respects, such as the elongation of the snout, the 

 position of the nostrils, the forward position of the articulation 



