244 CATALOGUE OF THE FOSSILS OF THE PERMIAN SYSTEM 
In Magnesian-limestone ; rare. Tunstall, Humbleton. 
It is more elongated than the Z. unioniformis of the Moun- 
tain-limestone. ‘The margins are also more nearly parallel, and 
it is of a smaller size. 
FAmiIny. SOLENIMYADZA. 
18. SOLENIMYA, Lamarck. 
1. S. ABNORMIS, 7. s. 
Shell transversely oval ; beaks not prominent ; posterior 
short, narrow, rounded ; anterior elongated, rounded, 
much wider than the posterior ; surface slightly waved 
concentrically, plain; muscular impressions obliquely 
placed, deep. 
In Magnesian-limestone ; rare. Tunstall, Silksworth. 
From the S. primeva of the Mountain-limestone, this species 
differs in being destitute of the radiating ribs so conspicuous in 
that species, and also in being less arcuated, and broader on the 
anterior portion of the shell. The anterior muscular impres- 
sions of this species are also larger and less obliquely placed. 
It is very rare. 
2. S. NORMALIS, n. 8. 
Shell, transversely oval, narrow, slightly arcuated ; beaks 
indistinct near the posterior end; anterior elongated ; 
muscular inypressions large, slight ; a few raised lines di- 
verging from the beaks to the free margins on the cast; 
external surface smooth. 
In Magnesian-limestone ; rare. Humbleton Hill. 
A single valve of this apparently rare shell was found in Hum- 
bleton quarry. It slightly resesembles the S. biarmica of the 
Russian Permian rocks, and another species from the Mountain- 
limestone of Northumberland, but the beak is near the posterior 
end, and the shell is narrower than it is in those species. It 
very strikingly resembles a recent species from the Mediterra- 
nean. 
