248 CATALOGUE OF THE FOSSILS OF THE PERMIAN SYSTEM 
22. LEDA, Schumacher. 
1. L. Vint, King. 
Nucula Vinti, King, Geol. of Russ. i., p. 224 ? 
In Magnesian-limestone ; rather rare. Whitley, Northumber- 
land ; Byers’ Quarry, near Souter Point. 
The anterior portion of this species is rounded and much more 
convex than the posterior, which is small and slightly rostrated. 
The surface is covered with numerous fine concentric lines of 
growth. It occurs in a thin bed of limestone in Whitley Quar- 
ries, and in a very thin crystalline bed near Souter Point. 
Famity. Myrinipa, Fleming. 
23. MYTILUS, Linneus. 
1. M. acumrnatus, Sow. 
Modiola acuminata, Sow., Geol. Tr., 2nd ser., 111, p. 119, 
No. 10. 
Mytilus Hausmanni, Goldf., Petrif., 138, f. 4. 
In Magnesian-limestone ; not rare. Tunstall, Humbleton, 
Silksworth, Dalton-le-dale. 
This common species is of an elongated subtrigonal form. 
The beaks are terminal and acute, furnished internally with a 
small pit or septum separated from the cavity of the shell by a 
thin plate. The hinge-margin is very much thickened internally, 
and the outer surface is covered with strong lines of growth. It 
is very common in some localities. 
2. M. squamostus, Sow. 
Mytilus squamosus, Sow., Geol. Tr., 2nd ser., fiii., p. 120, 
No. 11. 
In Magnesian-limestone ; not rare. Cleadon and Marsden 
Hill, Souter Point. 
This species is more ovate and less equivalved than the preced- 
ing. The surface is finely laminated. It is not so common as 
the former, and is generally very badly preserved. 
