EXTINCT BATEACHIA. 375 



Immediately in front of this wide scutum is the head, which has a differ- 

 ent form from that of the known species; although, viewed from 

 above, it is relatively as well as absolutely the widest in the genus, the 

 length being one-fifth less than the width behind, and the length of the 

 muzzle exceeding that of the orbits by one-fourth. The interorbital 

 width is two-thirds the long diameter of the orbit. The thinness of the 

 cranial bones prevents a determination of the structure of the skull, but 

 there is a flat, narrow bone in the position of ethmoid, and a scale-like 

 plate behind and below the orbit. 



The second specimen resembles the first in all essentials, including the 

 abdominal rods and thoracic scuta. It displays a slender but rather 

 elongate hind leg on each side, confirming again the definition of this 

 genus as possessed of hind but not of fore limbs. The femur is larger 

 than in other species, and is quite expanded proximately; one-half of the 

 tibia remains. 



Length to beginning of caudal fans, .065 m. ; length of head, .015 ; do. 

 to orbits, .006; do. of thoracic scuta, .007; width of thoracic scuta, .008; 

 do. of abdominal armature, .008 ; length of a caudal fan, .0025 ; do. of a 

 femur (No. 2), .0050; proximal width of do., 0015. 



Ptyonius Maeshii, Cope. 



Colosteus Marshii ; Trans. Amer. Philosophical Soc, XIV., p. 24. 



This species is represented by the type specimen and by parts of three 

 others, one of the latter including the pectoral shields. It is distin- 

 guished in the genus by the relatively large size of the dermal abdom- 

 inal rods, which are stouter and less numerous than in the other species. 



One specimen is lying on its back, displaying the ventral armature 

 somewhat disturbed, and broken through in some places. The head is 

 tufned abruptly to one side, and is apparently right side up. Several of 

 its elements are scattered on adjacent portions of the block. 



The head is of an ^ongate lanceolate form. The upper surface of the 

 frontal bones is punctate-rugose in relief, with short radii towards the 

 margin. The distal two-thirds of the mandible is narrow wedge-shaped ; 

 the external surface is coarsely pitted. There are no teeth preserved. 

 The sutures of the cranial bones are of the squamosal type, or fish-like. 



The three thoracic shields are considerably displaced. The lateral are 

 subtriangular, and are strongly ridged towards the inner margin. The 

 median shield is short spatulate, the narrow portion directed anteriorly ; 

 the posterior rounded. It is coarsely pitted medially, and coarsely and 



