14 ANATOMY OF VEETEBKATES. 



(Transitional) Order XI. PROTOPTEEI. 



Endoskeleton notochordal, partly cartilaginous, partly osseous ; 

 no occipital condyle ; vomer undivided ; temporal fossas roofed 

 over by bone ; pleurapopliyses short, with free extremities ; exo- ■ 

 skeleton as subcuticular cycloid scales ; scapular arch attached to 

 occiput ; proximal ends of hyoidean and tympano-mandibular 

 arches distinct. Vertical fin a continuous border to the com- 

 pressed tail. Pectoral and ventral fins svibulate, many jointed ; the 

 former fringed beneath ; the latter pelvic in position ; the pelvis 

 unattached to the spine ; gills filamentous, free, in a branchial 

 chamber with a single vertical outlet ; branchial arches imcon- 

 nected with the hyoid ; air-bladder double, lung-like, with air-duct, 

 glottis, and pulmonary vein. Prosencephalon predominant in 

 brain; nasal sacs snblabial with two remote extra-buccal aper- 

 tures ; auditory labyrinth in a distinct chamber ; bulbus arteriosus 

 long, with two longitudinal valves ; intestine with a spiral valve, 

 vent anterior to urethra ; ovaria distinct from oviducts. 



Fam. Sirenoidei. Ex. Lepidosiren. 



Subclass IV. Order XII. GANOCEPHALA. (Extinct.) 



Endoskeleton notochordal and osseous ; no occipital condyle ; 

 vomer divided ; temporal fossfe roofed over by Ixme ; hyoid arch 

 not connected with tymimnic pedicle ; branchial arches (?) un- 

 connected with hyoid ; exoskeleton as subganoid scales ; pleur- 

 apophyses short and free. Teeth with converging inflected 

 folds of cement at their basal half Pectoral and pelvic limbs 

 short, slender, three or four digitate ; natatory. 



Genus Dendrcrpeton. 

 Archcgosaurus. 



Order XIII. LABYRINTHODONTIA. {Extinct.) 



Head defended, as in Ganocephala, by a continuous casque of 

 externally sculptured and unusually hard and polished osseous 

 plates, including the supplementary "post-orbital" and "super- 

 temporal " bones, but leaving a " foramen parictalc." Two occi- 

 pital condyles. Vomer divided and dcntigerous. Vertebral 

 bodies, as well as arches, ossified, biconcave. Pleurapophyses of 

 the trunk, long and bent. Exoskeleton, in some, as smaH'o-anoid 



