44 Mr. R. Howse on the Permian System of the 



Remarks on the Species. 

 Brachiopoda. 



1. LiNGULA Credneri, Geiuitz. — The form of this shell as it 

 occurs in the marl-slate of Durham is a perfect oval, the breadth 

 being about two-thirds of the length. On our specimens the 

 roll-formed elevation is not so distinct as Geinitz represents it, 

 but the height of the valve increases from the posterior umbonal 

 margin to about one- third the length of the shell, whence it 

 decreases gradually towards the front and more rapidly towards 

 the sides. The lines of growth are strongly raised, and much 

 wider apart in front than in any other part. 



This shell is finely preserved in the marl-slate at Ferry Hill, 

 where it is rather abundant. The largest specimen I have seen 

 is half an inch in length and five-sixteenths in breadth, but it is 

 generally very much less. Only one individual occurred with 

 both valves together, and that was found in the compact lime- 

 stone a few feet above the marl-slate. Along with these, nume- 

 rous fragments of Fishes and specimens of Caulerpites selaginoides 

 constantly occur. 



I may be allowed to question the occurrence of this or any 

 other species of Lingula in the underlying red sandstone, as 

 stated in King's Monograph on the authority of Prof. Johnston, 

 as this sandstone is a true coal-measure stratum. 



2. DisciNA KoNiNCKi, Gciuitz. — Very little can be added to 

 the original description of this shell by Geinitz. The German 

 specimens appear to be of about the same size as those occurring 

 in England, and with the same proportions. This Brachiopod 

 has a greater vertical range in England than any of the others, 

 being found in the marl-slate, compact limestone, and shell- 

 limestone ; it is also the rarest. 



Geinitz observes, that as " neither the drawing nor description 

 of Schlotheim's O. spelunca?'ia appears to exist, the name which 

 Schlotheim gave to it should be suppressed." Mr. King has, 

 however, upon Goldfuss's authority, again revived it ; but until 

 some figure of it, or some description or specimen can be shown, 

 we have no right to adopt an apocryphal name. 



3. Productus horridus. Sow. — The exterior of this shell is 

 now very generally well known through the numerous figures 

 and descriptions of it which have from time to time been pub- 

 lished by several authors, but the interior has up to the present 

 period never been correctly delineated. Through the kindness 

 of Mr. Davidson, I am, however, furnished with four proof-plates 

 of Permian fossils, and favoured with permission to make refer- 

 ences to them ; in these the interior of this species is for the 

 first time faithfully represented. 



In the shell-limestone of Humbleton this species generally 



