Mr. T. R. Jones on some species of Leperditia. 87 



Norway/' Count Keyserling* states that this Gothland species 

 occurs in the Silurian dolomitic limestone on the Waschkina, 

 Petschora-Land, in company with another species (Leperditia 

 marginata, Keyserl. sp.). 



2. Leperditia Arctica, Jones. PL VII. figs. 1-5. 



Leperditia Balthica, var. Arctica, Jones. Salter's Appendix 

 to Sutherland's Journal of a Voyage in Baffin's Bay, &c., 1852, 

 vol. ii. p. ccxxi. pi. 5. fig. 13; and Quart. Journ. Geol. Soc. vol. ix. 

 p. 314. 



Dimensions of closed or of separate valves of four individuals : — 



Valves most convex near the centre, depressed near the mar- 

 gins ; antero- and postero-dorsal angles strongly marked ; the 

 anterior extremity acute. Central portion of the ventral border 

 of right valve projecting downwards with an almost angular 

 outline (giving the carapace a subtriangular shape), and over- 

 lapping the left valve to the extent of ^th of the breadth of the 

 carapace. 



Dorsal edge of left valve much thicker than that of the right ; 

 the thickness greatest posteriorly. 



Anterior and central tubercles well developed ; the radiating 

 vascular impressions form a delicate reticulation over nearly all 

 the inner surface of the valves, and arise from a large groove or 

 sinus surrounding the central tubercle. This circular sinus is 

 connected by a still broader sinus with the raised area of the 

 dorsal border of the valve. There is also another sinus em- 

 bracing the under side of the anterior tubercle, and passing for- 

 ward along the raised area in front of the tubercle to disappear 

 at the antero-dorsal angle. From the lower side of this sinus 

 fine vascular impressions originate, which freely inosculate with 

 the others. On one specimen (fig. 1 a) the anterior tubercle is 

 surrounded by a slightly raised, oval, crenulated border; and the 

 surface of the valve immediately beneath the central tubercle 

 distinctly exhibits by faint raised lines the course of the larger 

 radiating canals. 



Surface smooth and polished ; colour light brown. 



* " Wissenschaftliche Beobachtungen auf einer Reise in das Petschora- 

 Land." 4to, 1846, p. 289. 



