Counties of Durham and Northumberland. 49 



6. Strophalosia Cancrini, de Verneuil. — In England this 

 shell is best known as King's S. Morrisiana, in Germany it is 

 Geinitz's Orthothrix lamellosus, and in Russia it is the Prod. Can- 

 crini, de Vern. It may rejoice in more epithets than these, but I 

 am unacquainted with them. The one I have adopted is that 

 under which it was first described. Geinitz's name is next in 

 order, as his description and figures were published in the early 

 part of April 1848 ; and Mr. King's is last, as his specific de- 

 scription cannot date earlier than the appearance of his Catalogue 

 in August 1848. 



This species varies so much with age and locality, and is so 

 apt to become distorted, that no special form can be given 

 that will include all the individuals which undoubtedly belong 

 to it. In general, young individuals are broader than long — that 

 is, when the shell is of regular growth, — and the greatest breadth 

 of the shell is then very little more than that of the hinge- 

 margin. In larger individuals the general form is almost cir- 

 cular, and the hinge-margin appears narrower. In distorted 

 specimens the area is much narrower and deeper than in those 

 of regular growth. This is very remarkable in some specimens 

 from Tunstall. At Dalton this species resembles the form to 

 which Geinitz has applied the name lamellosus. The specimens 

 from Humbleton are much larger, and generally of regular 

 growth. I have never been able to detect spines on the upper 

 valve of any of the specimens from the above localities, but 

 Mr. Kirkby has lately obtained some individuals from Ryhope 

 with the spines distinctly shown on this valve. These specimens 

 are also rather broader than those from other localities, and the 

 striae are nearly obsolete. The most striking characters common 

 to all these forms are the long adpressed spines of the lower 

 valve, and the strong radiating striae which are generally present 

 on both valves. In old individuals the front margin strikes off 

 nearly horizontally, and forms a kind of siphonal tube in front. 

 There is also a tendency in this species to form a new internal 

 surface behind the old upper valve, for the purpose of con- 

 tracting the interior of the shell. It is not an additional, third 

 valve as King has supposed, for it is essentially connected with 

 the upper valve, and must have been formed by the upper lobe 

 of the mantle. 



Most plentiful in the shell-limestone of Humbleton, Tunstall, 

 and Dalton. In the compact limestone it is very rare. 



7. Orthisina pelargonata, Schloth. — This neat species is 

 not included in the list of Permian fossils of the ' Geol. Russ.' as 

 a British species ; and indeed, when I became acquainted with 

 some of our palaeontologists, I found them entirely unacquainted 

 with it. This was remarkably the case with Mr. King, who had 



Ann. ^ Mag. N. Hist. Ser. 2. Vol. xix. 4 



