12 SIRENOID AND CROSSOPTERYGIAN GANOIDS. 



Order GANOIDEI. 

 Sub-order Sirenoidei, J. Miiller. 1 



Diphycercal. Vertical fin continuous. Paired fins acute-lobate, if scale-bearing and 

 fringed ; archipterygian. Scales cycloid. Dentition of palatal and mandibular plates 

 with radiating ridges, and a pair of unopposed vomerine teeth. No gular plates or 

 branchiostegals. Mandible autostylic. Air-bladder a functional lung, and nostrils 

 opening into the mouth, in the recent species. 



Family Protopterini, Giintker? 



Paired fins long, slender, and pointed, supported by jointed, unbranched, cartilaginous 

 rods, with or without lateral rays. Bulbus arteriosus with two longitudinal valves. 



Genus Lepidosiren, Pitzinger. 



Skull imperfectly ossified ; no occipital condyles ; two long bones continued backwards 

 and upwards from the orbital region ; separated from these by muscles is a prominent 

 occipital crest. Nasal foramina double on each side ; anterior pair inferior, in front of 

 the mouth. Two ossifications of the opercular fold, which may represent opercular bones, 

 attached to the quadrate. Vertebral column notochordal ; neural arches ossified ; haemal 

 arches occur towards the tail. Upwards of fifty pairs of ribs. Pectoral arch imperfectly 

 ossified, connected with the ex-occipital bones above ; clavicles ossified, united below by 

 an epicoracoid cartilage. Pelvic arch cartilaginous, imbedded in ventral muscles, con- 

 sisting of a median cartilage, continued on each side into a cruciform curved process, to 

 the hinder ray of which the limb is articulated. Teeth. — Two pairs of opposed dentary 

 plates, each with three angular ridges, adapted for cutting, and separated by two angular 

 grooves. Anterior denticle ending in a sharp point ; posterior surface broader and less 

 elevated. Dentary plates consisting of dentine, and investing a bony base. Vomerine teeth 



1 ' Wiegm. Arch.,' 1843, p. 327. 



2 ' Phil. Trans.' vol. clxi, pt. ii, p. 555 (1872). 



