206 PROCEEDINGS OF THK GEOLOGICAL SOCIETY. [Dec. 14, 



On the Continent it was found at Vise, by M. de Koninck ; on 

 the banks of I'Ylytsch in the Ural, by Count Keyserling ; it also 

 occurs near Switschei, and at Sabl^ in France. 



EXPLANATION OF PLATE VIIL 



Illustrative of the Structure of the Shell-Valves qfChonetes and Productus. 



Fig. 1 . Chonetes comoides (Exterior), fi'om a very remarkable and typical 

 specimen belonging to the Bristol Institution Museum. In this 

 example the double area, trilobed cardinal process, and fissure are 

 largely developed : on the ventral area may be observed a series 

 of narrow diagonal concave strife, which diminish both in size and 

 distance as they approach the beak, and are similar to those already 

 noticed by Count Keyserling in his Russian examples. 



Fig. 2. Exterior of another individual, showing the concave dorsal valve. 

 The double area in this example is much less developed than in 

 fig. 1, but exhibits a similar cardinal process and fissures (the 

 margin has been slightly restored on one side). From the lime- 

 stone quarries under TreflachWoodatTrefonen, S.W. of Oswestrj', 

 Salop. This, as well as figs. 3, 4, 5, 6, 7, and 8, are drawn from 

 specimens discovered by and belonging to the Collection of 

 Mr. G. W. Ormerod of Manchester, and are regarded by Mr. 

 D. Sharpe as specifically distinct from fig. 1 ; but I feel disposed 

 to consider them as only varieties of C. comoides. 



Fig. 3. Exterior of the ventral valve. Same specimen as fig. 2. 



Fig. 4. A vertical section of the Chonetes, supposed to have been cut longi- 

 tudinally through the middle, exhibiting the comparative thick- 

 ness of the valves, as well as the remaining fi-ee space occupied 

 by the animal. 



Fig. 5. A fragment, exemplifying the great disproportional thickness of 

 the valves; along the weathered section of the ventral valve 

 may be distinctly traced successive layers of shell. This specimen 

 is from Tidenham Chase (Gloucestershire), near Chepstow. 



Fig. 6. Interior of the ventral valve of a broad specimen : (T) teeth ; (A) 

 flc^c/wc^or muscle ; (C) cardinal muscles. This beautiful specimen 

 was discovered on the beach at Beaumaris by Mr. Hemy Orme- 

 rod. (The margin has been slightly restored.) 



Fig. 7- A small, almost circular, example of the ventral valve, showing 

 the interior. This is figured to show an unusual development of 

 the central septum. From the same locality as figs. 2, 3. (The 

 sjDecimen is much damaged at the beak.) 



Fig. 8. A cu'cular example of the ventral valve. This specimen is similar 

 (although more perfect) to those from Llanymynech in the So- 

 ciety's Museum. It is from the same locality as figs. 2, 3. 



Fig. 9. Interior of the ventral valve of a Productus, perhaps giganteus, 

 from a remarkably beautiful and perfect example belonging to 

 the Bristol Institution Museum, and figured here to show the dif- 

 ference in the shape of the muscular scars compared mth those 

 of Chonetes. 



Fig. 10. Interior of the ventral valve of Productus horridus. 



Fig. 11. Interior of the dorsal valve of Productus longispiiius. to sen-e for 

 comparison with fig. 13, in which the same characteristic reni- 

 form impressions (V), supposed to be vascular, may be noticed. 



Fig. 12. Interior of the ventral valve oi a new species of Chonetes fromtlie 

 Devonian beds of Nehou, in France j exhibiting cardinal spines 



