PEXGELLY — i 



ON THE DEVONIAN AGE OF THE WORLD. 



343 



formed part of both the Silurian and Devonian faunas, was confined 

 to a very limited district in each period. 



Blastoidea and Grinoidea are the only orders of Echinodermata 

 found in Devon and Cornwall ; the first is represented by a single 

 species, Pentir&ribites ovalis, and this is only met with in the Barn- 

 staple area ; it occurs also in the Carboniferous period, as do all the 

 other species of the genus. 



Fourteen species of Grinoidea belonging to five genera and two 

 families have been found in Devon and Cornwall ; two of these occur 

 also in continental Europe in rocks of the same age, and five in car- 

 boniferous beds ; but not one seems to have been derived from the 

 Silurian series. Parts of the stems are extremely numerous occa- 

 sionally, both in the slates and limestones ; bodies are very much 

 less frequently found, and arms seldom if ever. Good examples of 

 the body of HexacrmiLS inter scapularis, but without stem or arms, 

 have been found in the TVoolborough quarry near Newton. 



Excepting Gijpridina serrato-striata, found at South Petherwin, all 

 the Crustacea of the two counties are Trilobites. No traces of Ptery- 

 gotus, Eurypterus, or Estheria — found in other British Devonian 

 localities — have been met with. The trilobites belong to ten species, 

 seven genera, and six families ; hence the genera and families are very 

 limited in specific development. With the single exception of Pha- 

 cops granulatus, found at Petherwin, they all occur in South Devon, 

 and are all confined to the Devonian era excepting Phillipsia Brog- 

 niarHi, which is also met with in carboniferous beds in many and 

 widely-separated European localities ; this was eminently a carboni- 

 ferous genus having no Silurian representative, but in all other cases 

 the generic affinity was with the Silurian age. Indeed, the trilobitic 

 form of life had passed its culminating point before the commence- 

 ment of the Devonian age of the world — the evening of the group 

 had already begun : no fewer than a hundred and seventeen species 

 had previously become extinct in Britain alone ; of these, ninety- 

 eight belonged to twenty-one genera and seven families, which had 

 also entirely disappeared from the earth. 



Pliacops latifrons occurs in the calcareous slates at Roseland Yale, 

 near Liskeard, in Cornwall, where it seems to have attained consider- 

 able dimensions : in many cases the eyes, though somewhat flattened, 

 are otherwise well preserved, not a facet being scratched. It has 

 also been found at Croyde and Barnstaple in North Devon, and in 

 clay-slate at Black Hall, near Totnes. 



The tail of Bronteus flabellifer is by no means rare in the limestone 

 of Woolborough, near Newton, and Lummaton, near Torquay ; no 

 part of the thorax seems to have been met with, but one example of 

 a tolerably distinct head with eyes was found at the former locality. 



Trimeroceplialus Icevis, the only British species belonging to the 

 genus, occurs under somewhat remarkable circumstances. So far as 

 is at present known, it has been found only in one locality, namely, 

 on the flanks of a hill called Knowles, near Newton, and no other 

 fossil of any kind has been seen there. On this point our knowledge 



