THE ANCIENT ROCKS OE ST. DAVID'S. 189 



This well-marked species can scarcely be confounded with any 

 other British species. Its very wide outer whorl, strong arched 

 striae, and compressed state are strongly characteristic and enable it 

 to be recognized at once. 



Locality and Formation. Llanvirn Quarry : Upper Arenig. 



Theca caereesiensis, n. sp. PI. XI. fig. 7. 



Description. — About If inch long by -f$ of an inch wide, apex 

 rounded. Surface covered with fine longitudinal lines. Lines of 

 growth very indistinct. A tolerably deep furrow down the centre. 



The presence of numerous fine longitudinal lines on the surface is 

 perhaps the most characteristic feature in this species. 



Locality and Formation. Llanvirn Quarry : Upper Arenig. 



Theca Harknessi, Hicks, Cambridge Catalogue. PI. X. fig. 11. 



This is a rather small species ; and the most marked character is 

 the presence of very strong cross striae towards the apex in addition 

 to longitudinal ones. 



Locality and Formation. Whitesand Bay : Middle Arenig. 



CONTTLARIA LLANVIRNENSIS, n. Sp. PI. XI. figS. 5, 6. 



Description. — From 6 to 7 inches long, and about 1J wide at the 

 larger end, conical, with tolerably straight sides and apex pointed. 

 One strong ridge down the centre of each surface. Lines of growth 

 rather indistinct. 



The single ridge down the centre distinguishes this species from 

 Conularia corium and G. Homfrayi, the only species likely to be 

 confounded with it. The former occurs in rocks of the same age 

 in North Wales, and the latter in the earlier groups in North and 

 South Wales. 



Locality and Formation. Llanvirn Quarry : Upper Arenig. 



Orthoceras caereesiense, n. sp. PI. XI. figs. 8-10. 



Description. — Probably at least 6 inches long and about 1 inch 

 wide at the broadest part. Striae arched gently backwards, fine and 

 closely placed. Shell very thin. This species approaches nearest 

 to 0. Avelinii, which occurs in rocks of the same age at Shelve, 

 Shropshire ; it differs from that species chiefly in being a wider form, 

 and in having the lines of growth much closer. 



Locality and Formation. Llanvirn Quarry : Upper Arenig. 



