176 THE GEOLOGICAL AGE OF CENTRAL AND WEST CORNWALL. 



It is evident that a great deal of work will have to be done 

 upon the Brachiopoda before they can be used to decide the 

 question Devonian v. Silurian, but there is at present at least as 

 much evidence for the latter as for the former. 



LAMELLIBTtANCIIIATxV. 



1. Aviculopecten pectinoides — {McCoy), Polruan. Cambridge 



collection. A Devonian species. 



2. A. D<(mnoniensis — |^ i/i? Co?/), Polruan ; Cambridge collection. 



Occurs in the rocks of S. Petherwyn and also at Mar- 

 wood and Baggy Point in Devon, being therefore an 

 Upper Devonian species. 



3. A. subradiata — {McCoy), Polruan; Cambridge collection. 



Occurs also at S. Petherwyn. 



4. Pecten sp. — (i/c Coy), Polruan. Cambridge collection. 



5. Pecten transversus. A specimen so named is in the Penzance 



Museum. 



6. Pterinea spinosa — [McCoy), Fowey. Sj)ecimen in Museum 



Pract. Geol. Lond., and in the Penzance Museum. 

 The lamellibranchiata recj^uire much more working out, but 

 at present they appear more Devonian than Silurian. 



GASTEROPODA. 



1. Acroculia sp. — Mellendreth, Peach I S44. Murchison gives 



the range of this genus as Llandovery to Ludlow. 



2. Turritella sp. — More probably a ITolopella. Polperro, Peach 



1844. Murchison gives examples of the genus from 

 CaradoG to Ludloio. 



3. Tjoxonema sp. — Powey, Peach 1844. Also at St. Columb, 



many well-known species have been recorded from both 

 the T>iiVonian and the Silurian. 



4. MurcMsonia sp. — Polruan, &c., Peach '847. Murchison 



gives the genus as characteristic of the Silurian sj^stem 

 from Llandeilo to Ljudloiv. 

 On the whole the Gasteropoda appear more Silurian than 

 Devonian. 



HETERORODA AND PTEROPODA. 



1. Belleroplion hilobatus — St. Columb Porth, Peach 1850. Mur- 

 chison gives its range as Llandeilo to Llandovery. 



