27 



apex is quite flat. There are about 20 rings in all, and 

 no tubercles down the smooth central portion. The sides 

 of tlie tail have 6 strong ribs, which are broad and some- 

 what flattened, divided from each other by narrow deep 

 furrows, and have the tips squarish and obtuse. The 

 ends of the four upper ones are free (or rather much 

 overhanging the margin) ; the remaining two are dis- 

 tinct nearly as far as to the margin, but they become 

 fused with those from the opposite side, and extend in a 

 very blunt point beyond the tip of the axis. The upper- 

 most ribs arch strongly outward, the next less so, and 

 tiie last i^air lie 2:)arallel to the axis. Externally the 

 whole surface of the tail is covered with a close sca- 

 brosity (figure 10). 



Variations — In the cast from Sholes Hook (fig. 12) 

 the rings on the axis of the tail are effaced down the 

 middle for a broader space, and there are but few of the 

 upper rings continuous aci'oss. Our figure in this case 

 does not show the ujjpermost rings. There are some- 

 times (fig. 11) seven rings on each side of the tail." 



Localities and Geological Range : Llandeilo Flags : 

 Rhiwlas and Llwyn-y-ci, north west of Bala Lake, etc.* 



Ceyptonymus raricostatus. Walcoti, 1877. 



Published in a Pamphlet Issued in Advance of the 29th Re- 

 gents' Report, N. Y. Cabinet, P. lb. 



"Pygidium subtriangular, convex ; length and breadth 

 about equal; anterior lateral angles truncated, so that 

 the lateral margins commence opposite the centre of the 

 pygidium. Axial lobe not very prominent ; crossed by 



* Copied from The Mem. Geol. Survey of the United Kingdom, Decade vii. 



