376 PALAEONTOLOGY OF OHIO. 



strongly radiate-ridged to the margin. Immediately behind these plates 

 the dermal armature commences. It consists of elongate, narrow, sub- 

 cylindric scales, which meet on the median line, converging anteriorly, 

 as in the long rod-like pieces of Oestocephalus. 



Nothing can be found pertaining to limbs ; but some laminae and im- 

 pressions in the position of pelvis, but not immediately connected with 

 the other portions of the skeleton, may belong to the latter arch. 



Length of body to buckler, 4.2 mm. ; width of ventral armature, .8 ; im- 

 pression of humerus (or coracoid), .2 ; length median thoracic plate, 1.15 ; 

 width do., .51 ; length fragment under jaw, .75 ; depth do. at middle, .15 ; 

 width end muzzle, .29. 



In a second and smaller specimen the fan-shaped neural spines are 

 seen to be developed in the dorsal region, though longer than high. The 

 median pectoral plate is a broad oval, with a lanceolate prolongation in 

 front. Behind it is subtruncate. Besides the radiating ribs, there are a 

 few tubercles medially. The chevrons of the abdominal armature are 

 separate from each other and continuous from end to end, thus not form- 

 ing a zigzag median longitudinal suture, as in Sauropleura longipes, etc. 



In another specimen the peculiar coarse ventral rods are associated 

 with the anterior part of the caudal series of vertebrae, with their fan- 

 shaped processes. The latter are about as broad as high, and have entire 

 margins and four or five shallow longitudinal grooves. A femur, with 

 tibia and fibula, projects from near the origin of the tail. They are 

 small, the femur measuring two fans of two caudal vertebrae along their 

 summits, or .004 m. The tibia and fibula are well separated. 



Other specimens present only ventral ossicles. 



Ptyonius Vinchellianus, Cope. 



Oestocephalus Vinchellianus; Proceedings Amer. Philos. Soc, 1871, 177. 



Represented by the opposite halves of a single specimen, which in- 

 cludes only the cranium and anterior half of the body.- The fan-shaped 

 neural spines commence but a short distance behind the line of the pec- 

 toral shields; they are low, and with a few coarse ridges; the margin 

 entire. The abdominal rods are delicate and hair-like. The pectoral 

 shield is an oval, with a few radiating crests, which originate at the cen- 

 ter ; in the areas between these there are a few scattered tubercles. The 

 lateral shields are ridged near the margin. 



The cranium is lanceolate in form, and the bones of the superior walls 

 are marked with a few raised points and ridges. There is a thin bone. 



