192 Proceedings of the Royal Physical Society. 



cording to the state of preservation. The space between the 

 outer margin and the inner ring is pierced by a series of 

 circular perforations, seven, eight, nine, ten, eleven, or twelve 

 in number. The margins of the perforations are plain and 

 non-serrated. The central space, when perfect, is occupied 

 by four smaller holes, but usually appears as a single large 

 vacuity. In the perfect plate the outline is somewhat undu- 

 lating, the undulation answering to the convexity of the 

 marginal perforations. On the under or concave side the 

 margin of these wheels is prominent and rini-like, and the 

 central portion also projects more or less. On the whole the 

 general appearance of these plates is very wheel-like, the 

 external rim or margin answering to the tire, the subdivi- 

 sions between the perforations to the spokes, and the central 

 four perforated space to the axle-hole. 



Several modifications have been observed, and will be 

 described later. 



d. Cross-like Bodies. — Associated with the foregoing remains 

 are spicules in the form of a cross with equal prolongations, 

 originating in a central body pierced by four holes in the 

 form of a triangle. The longest diameter of these measures 

 about "0215 in., while the apertures are about '001, or yoVo of 

 an inch. No other structure is visible, but they have the 

 same pellucid semi-transparent appearance as the hooks and 

 plates before described. The arms of the cross are sometimes 

 a little curved, and enlarged at their distal extremities. One 

 specimen has been met with in which two prolongations arise 

 from the central space, and at right angles to the other por- 

 tions of the cross in question. 



e. Other forms of Spicidar Bodies. — The remains described 

 in the foregoing passages are accompanied by two other 

 forms having the same mineral condition and general appear- 

 ance, but the affinities of which it is difficult to explain. 



The first of these resembles in form some fish teeth, 

 especially those of the genus Lamna. They are triangular 

 generally, but with the longer margins concavo-convex, ter- 

 minating above in a more or less acute point. In some the 

 concave side is serrate only, whilst in others both margins 

 are so. The surface appears to be slightly imbricato-striate. 



