1849.] NICOL ON THE SOUTH-EAST OF SCOTLAND. 53 



Pectunculus acuticostatus. Pl. X. fig. 13. 

 Testa suhorbicularis, subobliqua, postice subangulata, radiatim multicostata, costis 

 tenuibus, sulcisque angulatis ; area cardinal! bifariam tenuiter sulcata, dentibus 

 cardinalibus ad utrumque latus numerosis, confertis. 



A small species, distinguished by its subangular form posteriorly, 

 its angular radiating ribs, and its numerous close-set hinge-teeth. It 

 approaches in general form to P. Pallium, Reeve. 



Ostrea Haitensis. 



Testa oblonga, crassa, plicata, plicis paucis (senis ad septenis), magnis, undula- 

 tis, subsquamosis, squamis nonnunquam subtubulosis ; limbo intemo omnino 

 glabro. 



This species appears to be related to O. imbricata, Lam.; it dif- 

 fers, however, in its general form, which is oblong and not orbicular, 

 and in the number of external radiating folds, which are only six or 

 seven in our shell. 



Spondyltjs bifrons. 

 Testa subregularis, rotundata, -ventricosa, margine latiusculo, valide denticulate; 



extus radiatim costata, costis 5 ad 6 spiniferis ; area cardinali alterius valvse 



angustissima, alterius latiori. 



Nearest to S. imperialis, easily distinguishable by the area of one 

 valve being very narrow, and that of the other being rather broader, 

 though still narrow. 



2. Observations on the Silurian Strata of the South-East of Scot- 

 land. By James Nicol, F.R.S.E., F.G.S., Assistant- Secretary 

 Geol. Soc. 



During a visit to the south of Scotland last autumn I collected some 

 fossils from the older rocks of that district, which appear interesting 

 as adding another link to the chain of evidence by which the true age 

 of these deposits may be ascertained. Taken in connection with the 

 fossils formerly noticed* and with those procured by Mr. Moore in 

 Wigtonshiref, they may be regarded as rendering the Lower Silurian 

 age of one part of these beds almost certain, so that the connection of 

 the rocks and mountain-chains of this portion of Britain with those 

 of other countries may now be so far traced out. 



The fossils which Mr. Salter last year kindly determmed were 

 chiefly procured from the only bed of limestone known in the Silurian 

 rocks of the south-east of Scotland. My hopes of obtaining better 

 or more characteristic specimens from that locality were disappointed, 

 and not even a single new form was discovered after a careful search. 

 Indeed, the highly crystalline texture of the limestone, probably oc- 

 casioned by a mass of trap with which it is always associated, renders 

 it very improbable that this bed will ever add much to our knowledge 

 of the beings existing in the seas in which it was deposited. 



My researches in the slate rocks were more successful, especially in 

 the Grieston quarry near Traquair. In this place the rocks consist of 

 clay-slate, sometimes passing into a fine greywacke, and are wrought 

 * Quart. Geol. Journ, vol. iv. p. 205. f lb. vol. v. p. 7. 



