88 Mr. T. R. Jones on some species of Leperditia. 



L. Arctica occurs abundantly in the Upper Silurian limestone 

 at Cape Hotham in Assistance Bay, and Seal Island in Baring 

 Bay; also in Griffiths and Cornwallis Islands. Specimens were 

 brought to England by Dr. P. C. Sutherland. 



This species (which at first, when Mr. Salter showed it to me 

 in 1852, I was scarcely disposed to separate from the Gothland 

 species) differs from L. Balthica in several points, — in its smaller 

 size, — greater angularity of outline, — the greater convexity of 

 the valves, and depression of their dorsal region, — the thickness 

 of the dorsal edge of the left valve, — the great overlap of the 

 right valve, — the greater delicacy and extent of the radiating 

 canals, — and the lighter colour. 



3. Leperditia alta, Conrad, sp. (?) PI. VII. figs. 6 & 7. 



Cytherina alta, Conrad, Report Geol. New York ; Vanuxem, 

 Geology of New York, 1842, p. 112. fig. 23, 6; Hall, Palaeon- 

 tology of New York, 1852, vol. ii. p. 338. pi. 78. fig. 2 a, b, c. 



A specimen of hard, dark Upper Silurian limestone, containing 

 numerous specimens of Leperditia, chiefly on a weathered plane 

 of bedding, was brought to England from the shores of Wel- 

 lington Channel * by Dr. P. C. Sutherland, and is now in the 

 Museum of Practical Geology. The fossils are single valves, 

 with their convex surfaces more or less exposed on the weathered 

 surface, which also presents numbers of minute bodies, probably 

 crustacean likewise. The valves are roughened by the irregular 

 dissolution of their substance, and each has the most prominent 

 spot of its convexity irregularly enamelled, as it were, by a local 

 miueralogical condition of the altered calcareous matter of the 

 fossil. The limestone affords a few specimens by fracture ; these 

 have smooth surfaces. The characters are as follow : — 



Dimensions of separate valves of five individuals : — 



Length. Breadth, 



(inch) (inch) 



5 J_-> 



2^ 2 4 



^ -1 >Left valves. 



10 _6 J 



2% ^^\ Right valves. 



2¥ ¥¥-• 



Carapace-valves strongly convex, smooth, dark olive-brown in 

 colour, more or less oblong, somewhat variable in outline, straight 

 above, rounded below ; extremities obliquely rounded ; the 

 dorsal angles in some much more definite than in others ; pos- 

 terior half broader and rounder than the anterior. Anterior 

 * Cape Riley or Beechey Island. 



