Counties of Durham and Northumberland, 47 



Shell gryphcBoidj concavo-convex ; lower valve convex, bilobed, or 

 with a slight furrow or sinus in the centre ; upper valve slightly 

 concave, or nearly flat ; beak of lower or convex valve large, and 

 very much flattened ; hinge-line of upper valve rather angulated, 

 furnished with a large triangular button ; surface of convex valve 

 covered with a few distant spines. 



The above description was drawn up from a cast, PI. IV. fig. 3, 

 which Mr. Davidson has recently figured, Mon. Brit. Brach. 

 pi. 4. fig. 5, and which Mr. King had the loan of, with all my 

 other Permian Producti, for a considerable time. The discovery 

 of a large series of specimens at Tunstall in a fine state of pre- 

 servation enables me, through the liberality and kindness of Mr. 

 Kirkby, to add a few more particulars to the above description. 



The general form is subquadrate, somewhat compressed when 

 seen laterally, but in full-grown specimens it has a considerably 

 produced frontal margin. The lower valve only is covered 

 sparingly with spines of great length ; some that I have seen 

 extend more than two inches from the shell. The hinge-margin 

 of this valve is very much thickened by lines of growth, so as to 

 lead one to suppose that it is furnished with an area, but it is 

 not. A small triangular aperture, open from the very apex, 

 receives the sharply-pointed triangular boss of the upper valve. 

 This sharp point leaves a little, narrow groove as the shell in- 

 creases in growth. But there is no proper area, foramen, or 

 deltidium to be seen, — nothing, in short, to warrant its removal 

 from the genus Froductv^. 



It differs from its congener in several important particulars. 

 The boss or muscular fulcrum, the shape of the muscular im- 

 pressions, the greater size of the oral arms, the absence of car- 

 dinal spines on the upper valve, the flanging of the hinge-margin 

 of the upper valve, are so strongly characterized, that it cannot 

 be mistaken for any other species. 



Mr. King has given to this shell another name, for the priority 

 of which he refers to his catalogue. As I shall state my claims 

 of priority elsewhere for my catalogue, it may be permitted me 

 to remark here, that this shell is not specifically described in 

 Mr. King's catalogue. It occurs in the shell-limestone only, in 

 which I have taken a fine series at Dalton, and Mr, Kirkby at 

 Tunstall Hill. 



5. Strophalosia Goldfussi, Miinst. — To this characteristic 

 but variable species I now refer all the StrophalosicB, which have 

 been separated into two groups by all who have written on Perm- 

 ian shells. I was of this opinion before I became acquainted 

 with Geinitz's ' Versteinerungen / but from the characters given 

 in that work and Mr. King's Monograph, and an excellent series 

 of these forms collected by Mr. Kirkby and myself, I am in- 



