NORTHUMBERLAND AND DURHAM. 251 



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, re- 

 ceives 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 Productus. 



It differs from P. liorridus in several important particulars. 

 The cardinal-process, the shape of the muscular impressions, the 

 greater size of the oral arms, the absence of cardinal spines and 

 the flanging of the hinge-margin of the upper valve, are so 

 strongly characterised that it cannot be mistaken for the above 

 or any other species. 



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

 of which he refers to his catalogue. As I have stated the claims 

 of priority for my catalogue elsewhere, 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. Herr Schubarth has found it in the equivalent 

 deposit near Possneck. 



5. STROPHALOSIA, King. 

 1. S. GoLDFUssi, Milnst. 



To this characteristic but variable species I now refer the 

 Strojyhalosi'ce, which have been separated into two groups by al- 

 most all who have written on Permian shells. I was of this 

 opinion before I became acquainted with Geinitz's " Versteine- 

 rungen 5" but from the characters given in that work and Mr. 

 King's Monograph, and an excellent series of s^iccimens col- 

 lected by Mr. Kirkby and myself, I am obliged to abandon this 

 idea, and to include both forms in one specific gronp. 



The OrthotJu'ix Goldfussi of Geinitz is considered the typical 

 form. It is the Strophalosia excavata^ King ; and Stropli. 

 Goldfussi, King, is without doubt the 0. excavaius, Geinitz, as 



