106 DESCRIPTION OF FOSSIL SPECIES. 



Found at Helensburgh, by Mr Smith. 



" I believe a new species. I am acquainted with it as a living 

 species, occurring in the North Sea, and as a fossil in the recent for- 

 mations in Sweden." — Deshayes. Mr Sowerby considers it identical 

 with a recent species from Behring's Straits. It is perhaps the most 

 common of the fossil shells of the Basin of the Clyde, but I have not 

 met with it in any other locality. — S. 



14. MACTRA STRIATA. N. S. — Smith. 

 Plate I. Fig. 22. 



Shell subtriangular, concave, with nearly equal sides ; umbones 

 central, and slightly turned to one side ; lateral teeth prominent ; 

 inside smooth ; external surface with very strong, concentric strise ; 

 length seven-eighths of an inch ; breadth an inch. 



This species might be mistaken for the Mactra subtruncata, having, 

 like that shell, strong concentric strise ; but it is totally different in 

 contour, being more triangular, more equilateral, and not produced 

 on the anterior side like that species. — B. 



Found at Stevenston, Ayrshire, by the Rev. Mr Landsborough. 



DESCRIPTION OF PLATE II. 



RECENT SPECIES. 



I. PECTEN JAMESONI. N. S. — Smith- 



P. testa sub-sequivalvi, suborbiculari, longitudinaliter undulato- 

 plicata, striata, plicis 4-5, auriculis .insequalibus. Lon. § un. Lat. f . 



Allied to the Pecten polymorphus of Bronn (Phillippi, p. 79, tab. 

 v. figs. 18, 21), but differs in several respects, especially in the in- 

 equality of the auricles. The longitudinal striae vary much in 

 coarseness ; the upper valve is somewhat larger than the lower ; the 

 auricles are ribbed and striated by lines of growth ; the longitudinal 

 ribs or folds vary much in convexity, and are sometimes acutely 

 carinated. The colour is white, with a tinge of red, especially near 

 the beaks. Very distinct from any recorded British Pecten. — F. 



Dredged at Bute by Mr Smith. 



2. PECTEN LANDSBURGI. N. S. — Smith. 

 P. testa subsequivalvi, suborbiculari, radiis minimis longitu- 

 dinaliter rugoso-striatis, striis transversis regulariter undulatis, auri- 

 culus insequalibus. Lon. £ un. Lat. T 5 5 un. 



A very beautiful species, allied to Pecten obsoletus, first observed 

 by the Rev. Mr Landsborough, on the coast of Ayrshire, afterwards 



