1846.] MORRIS AND SHARPE ON FALKLAND ISLANDS FOSSILS. 275 



crossed by a few concentric lines of growth. Hinge area linear, of 

 the breadth of the shell; hinge line furnished with fine spines. 

 Width I" of an inch, length ^ an inch. 



This shell so closely resembles some of the forms of the Chonetes 

 sarcinulata {LeptcBua lata, Sil. 8yst.) of the Ludlow rocks, that, if 

 found in England, it might probably have been mistaken for a va- 

 riety of that species ; it is however somewhat flatter, more square 

 and rather larger. The spines on the hinge line are not well pre- 

 served in the specimens examined, but traces of them may be di- 

 stinctly seen. The C. Falklandica may be considered as belonging 

 to the same group as C. sordida, C. Hardrensis, C. Buchianai all 

 of which are closely-allied species to the C sarcinulata, 



2. Orthis Sulivani, sp, n. PI. X. fig. 1. — Semi-ovate ; ventral valve 

 nearly flat, dorsal valve gibbose ; surface covered with fine sharp 

 bifurcating striae, increasing towards the margin toa bout 150, 

 crossed by 3 or 4 concentric lines. Hinge line neatly as wide 

 as the shell, hinge area broad and triangular. Interior of both 

 valves striated for about \ of an inch round the edge, producing 

 a fringed appearance in the cast. 

 Width l-f- inch, length 1-i-inch. 



There is a slight resemblance between this species and the Atrypa 

 reticularis of the Silurian System ; it is however a true Orthis and 

 has a finer striation than that shell ; in the latter genus it is most 

 nearly related to an Orthis common to the Coniston, &c. beds of the 

 Silurian formation, about to be described and figured by Professor 

 Sedgwick. 



This species has been dedicated to Captain Sulivan, who was em- 

 ployed in the survey of the Falkland Islands, and who materially 

 contributed towards the enlargement of the geological collection 

 from them. 



3. Orthis tenuis, sp.n, PI. XL fig. 4. — Nearly semicircular; both 



valves flat and covered with fine bifurcating striae, increasing 

 to about 200 at the margin, and crossed by a few concentric 

 lines. Hinge area of the width of the shell, linear. The cast 

 is scarcely thicker than a sheet of paper and faintly marked by 

 the striae. 



Width \\ inch, length \ of an inch. 



Nearly allied to the Orthis expansa and O. grandis of the Lower 



Silurian rocks. 



4. Orthis concinna, sp.n. PI. X. fig. 2. — Semi-oval; both valves 



slightly convex, covered with very fine bifurcating striae, in- 

 creasing to about 120 at the margin, and crossed by a few con- 

 centric lines. Hinge area of the width of the shell and nearly 

 linear. 



Width 1 inch, length f of an inch. 



This species is closely allied to the Orthis tenuis, but it is less flat 



and of a more rounded form. 



