THE GEOLOGICAL AGE OF CEKTRAL AXD WEST CORNWALL. 169 



" This species exists as a brown friable mass, but in some cusps retains the 

 character of the surrounding- stone. The number of the longitudinal ridges 

 varies from 40 to 42— at St. Columb to 44-at Fowey to 48. Some of these ridges 

 run uninterruptedly from thfi base to the apex ; while others ascend about one- 

 third of its height and divide into two lamella;. The furrow between these 

 ridges is narrow, and frequently occupied by tubular projects which are irregular 

 in their distribution. The apex is truncated and excavated. This species is 

 most frequently very much distorted by violent compressions and contortions, 

 and hence assumes a vai-iety of shapes ; and the finer raarkings, such as the 

 denticulations of the lamella, are freciueutly obliteratsd. This, as most others 

 in the Cornish slates, exists chiefly in casts "—[CourJi, Trans. Roy. Geo. 

 Soc. Cor., VI, p. 276). Respecting the same species Milne-Edwards says "the 

 septa, to the number of 36 or 48 must have been alternately of unequal size, the 

 principal ones extending to the centre of the visceral chamber, where they became 

 somewhat twisted. Brif. Foss. Corals. 



2. C. pauciradialis,= C. Una pars. {Milne-Edwards) v. Phillips, 



Pal. Foss, pi. 1, fig. IF. Is given by some authors as a 



mere variety of the preceding — occurs at Fowey and 



Polruan, as recorded by Couch, 1846. 



" This species is more frequently of the character of the surrouu'ling 

 rock than the last, and it is smaller, and the ribs ai'e about 20, acute aud 

 thin. Most of the lamella; extend from the base to the apex but a few others 

 extend to various heights. The sulcus is wide ; the delicate serrations of the 

 lamellfe are frequently destroyed. In the centre of the ribs of some specimens is 

 a depression, on each side of which is a row of small raised tubercles." — (Couch, 

 loc. cit.) 



3. C. j9/M;'?VffvZ/rt/?'s= C. 5m« j9«rs. {Milne- Edwards) «. Phillips, 



Pal. Foss., pi. II, fig. o. — Fowey, Polruan, Pridmouth, 

 Gribben; (Peach 1844, Couch 1846.) 



" The external surface is marked by from 68 to 80 longitudinal striaa, 

 most of which run from the base to the apex, with occasional smaller and shorter 

 ones with circular undulations. In the furrows are a few scattered tubular 

 projections. The reverse of this description must be taken in the brown casts ; 

 for the grooves in the first ai-e represented bj^ the lamellre in the second. The 

 appearance of the lamelliB depenrls very much on the age and size of the 

 specimen. In the young, the lamella; are fewer in number, and the secondary 

 ones shorter and more widely sep.irated than in the older. This species is also 

 frequently very much compressed aud distorted by former convulsions and 

 movements of the rocks." (Couch, loc. cit.) 



4. C. elongata= C. hina pars. {Milne-Edwards) — Fowey and 



Polruan, according to Peach and Couch. Murcliison 



says this species ranges from the Caradoc to the 



Llandoverg. 



" This is rathor more a columnar than a f ouoidal species ; it is undulatclj' 



elongated with faint traces of annulations. The stria; are numerous, aud closely 



arranged ; many of them extend from the base to the apex, while othi rs are 



shorter ; but all Cornish specimens hitherto procured are so obscure aud distor'ed, 



that a detailed description cannot be taken from them." (Couch, loc. cit.) 



