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DK. A. VAT7GHAN ON THE PAJ^EONTOLOOICAL [May I905, 



I have not, as yet, sufficient material to be justified in assigning 

 the Bristol forms to definite species. 



The specimens agree with the definition of Eumetria in : — 



(1) The form and the absence of mesial fold and sinus. 



(2) Purely radial ribbing, without distinct axial symmetry. 



(3) Alate cardinal extremities in the brachial valve. 



(4) The elevated cardinal area, formed laterally of two concave, narrow 



strips, which are separated from the rest of the valve by strong ridges. 



(5) The triangular delthyrium and the foramen. 



All the specimens are much smaller than the form figured by 

 Davidson, and Davidson's figure is moreover unreliable, as it is 

 merely a restoration of a very poor specimen * (which is preserved in 

 the Museum of Practical Geology, Jermyn Street). 



Camarotcechia. 



CAMAEOT03CHIA MITCHELDEANENSIS, sp. nOV. (PI. XXVI, figS. 7-7 h 



& text-fig. 6.) 



External characters. — Shell small and slightly transverse; 

 medial area of brachial valve flattened on the fold ; median line of 

 each valve strongly convex near the beak, but becoming less and 

 less curved until, near the frontal margin, it is almost straight. 



Fig. 6. — Brachial valve of Camarotcechia mitcheldeanensis : 

 plan of hinge-region. 



s = Mesial septum, splitting into two sheets near the beak, and supporting 



the hinge-plate along the suture-line dd. 

 x = Gap between the hinge-plates, which are in contact below (this gap is 



probably exaggerated in the specimen figured). 

 hp — The hinge-plates, from which the crural bases (c) project. 

 b = The sockets (crenulated). 



Fold and sinus well marked ; their line of intersection deeply 

 trapezoidal. Ribs angular, nearly straight, prominent from beak 

 to margin, and separated by deep angular furrows ; three (less 

 commonly four) ribs on the fold ; two (less commonly three) ribs 

 in the sinus ; five or six ribs on either flank of each valve. 



1 This specimen was obtained from Skrinkle Bay, and therefore from the 

 same horizon as the Bristol forms. 



