LOWER SILURIAN' ROCKS NEAR WELSHPOOL, WALES. 



Fig, 2, — Tliainniscus antiquus, Sj9, n. 



111 



A. The specimen, enlarged 2 diameters, 



B, C, D. Details more highly magnified. 



2. Thamniscijs antiquus, sp. n. Fig. 2. 



Zoarium apparently springing from a root-like base, strong and 

 thick towards the bottom, where several root-branches appear to be 

 united, more delicate towards the younger or growing portion of 

 the zoarium. Branches frequently dichotomising, free. Zocecia 

 tubular, shown on one side only of the branch. Tubular cells not 

 contiguous, rather broad at the openings, gradually thinning out 

 towards the axial region of the zoarium : cell-mouths, so far as I 

 can make out, rather elongated, peristomes not prominent, reverse 

 striated ? 



Formation. Imbedded in volcanic ash, probably of the age of 

 the Bala rocks. 



Locality. Middleton Hill, near "Welshpool. 



Cahinet. J". B. Morgan, Esq., Welshpool; one specimen. 



This beautiful specimen, which I have drawn magnified about 

 four diameters, is buried in volcanic ash, which is so friable that it 

 breaks away with the least touch. It is very certain that it is the 

 reverse surface that is exposed ; but towards the bottom the thick- 

 ened branch is broken away, and the cells are exposed. The 

 appearance of the branch at this part is shown in fig. 2, b ; 

 but when more highly magnified the arrangement of the cells is 

 seen to be pretty regular, and is shown in fig. 2, c. By extracting a 

 minute fragment of the specimen from the matrix, I have been able 

 to expose the poriferous surface, and this is shown in fig. 2, d. 

 So far as I am able to judge by carefully manipulating this delicate 

 fossil, I can almost confidently assert that the species now described 

 dijffers considerably from the species previously described by myself * 



Quart. Journ. Greol. Soc. vol. xxxviii. p. 



k2 



