522 H. H. SWINNEBTON. 



cartilage. In the Cliaracinidte (Sageniehl^ 85, p. 14) and 

 Cyprinidee (ibid., 91, pp. 497, 499) every gradation exists 

 from the condition here shown in the young stickleback to 

 that found in the Scomber (fig. 44, e. m.), in which, as in the 

 majority of Teleosts, this bone has lost all sign of a 

 membranous origin, and consists entirely of ossified mes- 

 ethmoid cartilage. 



All the cranial membrane bones are now present. 



Adult. — In assuming the adnlt condition the chondro- 

 cranium undergoes but little change, beyond a continuation 

 of those ossificatory processes which had already set in at 

 the last stage. Consequent!}', the cai'tilaginous portion is now 

 confined mainly to regions where primary ossifications have 

 met and formed sutures, and to the ethmoid region, where 

 it is still moderately massive. 



Its upper and under surfaces are sharply marked off from 

 one another by a plane in which lie the pre-ethmoid region, 

 the parethmoid, and a conspicuous ridge running along the 

 middle of the sphenotic and pterotic bones. The upper 

 surface does not present that strongly crested and grooved 

 appearance so characteristic of Teleosts, but is perfectly even 

 from end to end and from side to side. It thus presents a 

 condition comparable to that of Amia. The temporal fossa 

 is a shallow uncovei-ed depression, and, as in Amia, is the 

 only portion of the dorsal surface upon which trunk muscles 

 encroach. The rest of the roof is covered by a thin skin. 

 A further similarity to the Amioid or Ganoid condition is 

 seen in the fact that the surfaces of all the roofing bones 

 are beautifully sculptured and polished (PI. 29, fig. 18), the 

 rugas on any one bone generally radiating from a central point. 

 This sculpturing is a feature by no means universal among 

 Teleosts, and those forms in which it does occur to any 

 appreciable extent are frequently among the lowliest of the 

 gi'oup to which they belong; e.g. Erythrinus and Sarcodaces 

 (Sagemohl, 85, p. 34) among Characinida3, Avaparinui among 

 Malacopterygii, and to a lesser degree Sphyrsena among 

 higher Teleosts. Nevertheless the condition in such a form 



