Mil. T. ATTHEY ON PTEEOPLAX COllNUTA. 183 



of an inch, in breadth one inch and one-tenth, in length one 

 quarter of an inch ; its sides are slightly excavated, it is bi-con- 

 caye, and has a small notochordal foramen. One of the processes, 

 a transverse one, is six-tenths of an inch long by the same in 

 breadth, and is much crushed. A zygapophysis is present, but 

 too much injured to admit of description. The remaining pro- 

 cess is of about the same size and in the same condition. 



Rihs. — On the same piece of shale there are fragments of three 

 ribs ; the proximal ends of two are present, and, though much 

 flattened, show well the head and tubercle ; the distal end of the 

 third exists, but is much flattened. It is the under surface, some- 

 what concave, which is exposed. In close relation with the head 

 are three portions of ribs : one large fragment, showing head, 

 tubercle, and groove, lies on the left side of the cranium ; another 

 fragment with head and tubercle lies obliquely under the cra- 

 nium ; a short piece of the sternal end of a rib rests in part on 

 the occiput. 



These are shown in Plate XY. The first is five inches and a 

 half long, by three-tenths of an inch broad ; it is well and regu- 

 larly arched; the curve of the bone is continued as far as the 

 head, which ends in a concave articular surface ; the tubercle, 

 four-tenths of an inch posterior to the head, ends likewise in a 

 concavity for articulation. A groove runs along the under sur- 

 face from near the tubercle for two-thirds of the length of the 

 rib ; beyond this the surface is flattened. 



The head, tubercle, and part of the groove are seen on the rib 

 which lies under the cranium. Nothing is worthy of note with 

 regard to the third fragment, which may be a part of the first- 

 named. 



These ribs, lying in contact with the skull of Pteroplax, must 

 be taken as having belonged to the same animal. 



The ribs imbedded on a piece of shale cannot, perhaps, be 

 proved to have belonged to Pteroplax ; but they are of the same 

 size, and arc in other respects very like those on and under the 

 cranium, and were found in the same part of the mine. 



If this inference be correct, then the vertebra) lying with the 



