264: NOTES ON THE I'ERMIAN SYSTEM OF 



cimeiis from the upper beds that this character is shown to per- 

 fection, hut it may he traced on very many specimens from the 

 shell-limestone. 



The existence of this mytiliform shell in such great plenty in 

 the shell-limestone, and its generally rough and stunted appear- 

 ance, would seem to lead to any other than the conclusion that 

 tliis deposit of shell-limestone was of "pe/a///c" origin. The 

 entire fauna of this limestone is indeed so decidedly littoral in 

 character, and so clearly of shalloAv-water origin, that I could 

 not, many years ago, refrain from pointing it out, and no state- 

 ment has been made since that invalidates this conclusion. 



This species is most abundant in the shell-limestone, and 

 occurs sparingly in many of the upper beds of limestone. 



18. MACRODON, Lycett. 

 1. M. STRIATA, Schlotll. 



The form of the teeth of this shell agrees with that of Macro- 

 don, Lycett, and Morris, and the general shape is also very 

 similar. The hinge-area is often very much developed in speci- 

 mens whose growth is somewhat stunted round the free margins 

 of the shell. This is the form best known in England, {Area 

 tumida, Sow.) The regularlj^-grown shell is one of the most 

 beautiful, both in form and ornament, of those from the Permian 

 rocks. Tlie smooth or j^artially smooth examples described as 

 a species (A. Kingiana), can often be traced on the umbonal re- 

 gions of genuine M. striata. The specimens figured in the 

 " Perm. Mon." give a very poor idea of the shape and beauty 

 of ornamentation of this common characteristic S23ecies. 



In the shell-limestone, rather common at Tunstall, and occur- 

 ring frequently in all the localities mentioned in the Table. It 

 appears to be a much commoner species in England than in 

 Germany. 



19 LED A, Schumacher. 



1. L. SPELUNCARIA, Geiuitz. 



It is not to be disputed that Geinitz's figure and short de- 

 scription of this little shell have priority over Mi-. King's; 



