EXTINCT BATEACHIA. 377 



which I have^ already alluded to as the squamosal or preoperculum, 

 shaped like a right-angled triangle, separated from the outer posterior 

 angle of the head, which exhibits a few similar marks. 



Length of cranium, 0.020 m. ; width of do., .008; length median pecto- 

 ral plate, .0042. 



This small species is of the size of P. pectinatus, and should be 

 especially compared with it. In specimens of that species in which the 

 cranium has the same size, the median pectoral plate is narrower and 

 more prolonged longitudinally, and exhibits tubercles and a few ridges 

 near the circumference, but no cross like figure. 



Dedicated to Prof. Alexander Winchell, of the University of Michi- 

 gan, author of that interesting work, Sketches of Creation. 



Ptyonius PECTINATUS, Cope. 



Sauroplaira pectinata, Cope; Proceed. Acad. Nat. Sciences, 1868, 216. 

 Oestocephalus pectinatus, Cope; Transac. American Philos. Soc, XIV., p. 20. 



Represented in the collections by eight characteristic and perhaps 

 two other individual specimens. These furnish material for a pretty 

 full account of it, though it is to be regretted that while two have the 

 crania, the constitution of the superior face is not easily made out. 



The head is lanciform, and the muzzle very elongate, slender, and 

 acute at the extremity. The orbits are behind the middle of the length, 

 and are large ; they narrow the frontal region, so that it is narrower than 

 the diameter of either. The cranium is truncate behind, and the angle 

 of the mandible projects a little beyond it. The posterior portion of the 

 mandible is strongly sculptured ; on the upper half there are inter- 

 rupted longitudinal ridges; on the lower the elevations predominate 

 and inosculate, leaving intervening pits. The angle of the mandible is 

 acuminate. In one specimen a bony plate in the position of the squa- 

 mosal is striate in the direction of the axis of the head. The teeth 

 are conic and acute, and some of them larger than the others and striate 

 longitudinally. In one specimen a close series of minute conic teeth 

 passes across the upper part of the orbit, indicating the existence of a 

 palatine or pterygoid dentition In one specimen the preserved surface 

 of the bone which constitutes the postero-external cranial angle is 

 sculptured with rather distant impressed pits. The thoracic shields are 

 well preserved. The median is a narrow oval, with anterior and poste- 

 rior prolongations. In one specimen it is marked by a limited number 

 of tubercles, arranged radially round the vacant center ; in another the 



