PLATE 10. 
Pago 
Pigs. 1-26. Streptorhynchgs chemungensis. 67 
1. A dorsal valve of symmetrical proportions, which has a convexity a little greater than that 
of the ordinary specimens of S. pandora in the Corniferous limestone. The striae are 
bifurcate, and in their partially preserved condition, are unequal at the margin of the 
shell; a few finer ones between the larger reaching half or two-thirds the way to the apex. 
2. The exterior of a ventral valve which is nearly flat, being slightly concave below the middle; 
the apex is prominent and very slightly unsymmetrical. 
3. A cast of the same valve stowing the muscular impression. 
4. The exterior of a dorsal valve which is regularly convex; the striae are sharply elevated and 
fasciculate, there being two or three finer ones between the stronger and more elevated ones. 
5. A cast of the interior of the same valve showing the muscular and vascular impressions. 
6. A dorsal valve of moderate convexity with one of the cardinal extremities abruptly rounded,and 
the other distorted, apparently from some accidental cause. The stria} are fasciculate, 
there being one, two or three finer ones between the stronger sharply elevated ones on the 
lower half of the valve, while towards the beak they are all sub-equal. This is the origi¬ 
nal of Strophomena pectinacea. 
6 a. An enlargement of striae, from specimen fig. 6, S. pectinacea. 
7. A convex dorsal valve with the cardinal extremities slightly rounded; the striae are, in some 
parts, sub-equal, and in others alternating in size, and the stronger ones are sometimes 
interruptedly depressed. The mesial portion of the valve is flattened The specimen 
shows the striae curving upward to the hinge line in a most remarkable degree. 
8. The cast of a large and very convex dorsal valve with the extremities abruptly rounded. The 
surface is unequally striated. The umbo is large and very prominent, while the surface 
below the umbo to the front is somewhat depressed convex, and abruptly depressed on 
each side, leaving the space between that part and the hinge extremities concave. This 
specimen may be compared with fig. 26, Plate 9, from the Corniferous limestone. 
9. A cardinal view of fig. 8. 
10. A slightly concave ventral valve where the striae are sub-equal and bifurcating, or increas¬ 
ing by interstitial additions. The character of striae is precisely similar to those of 
the Corniferous limestone specimens of S. pandora. 
11. A dorsal viewin which thestriaeare sharp and sub-equal; of the type of Strophomena arcto- 
striata. 
12. A specimen of similar character which is extremely unsymmetrical. 
12 a. An enlargement of the striae which characterize the specimens like those from 11 to 17. 
13. A ventral view of an unsymmetrical specimen. 
14. A cardinal view of the preceding specimen. 
15. A profile of the same. 
16. A cardinal view of specimen when the apex is less extended. 
17. A profile of fig. 16. The specimens 11 to 17, are of the type of Strophomena arctostriata, 
showing various degrees of distortion. 
-.18. A ventral valve with rather deep and coarse striae. 
jl9, 20. Casts of dorsal valves of nearly symmetrical forms. 
21, 22. Casts of ventral valves. 
23. A cardinal view of a cast of a large ventral valve which is symmetrical on the hinge line. 
-24. The cardinal process from a gutta-percha cast from specimen fig. 9. 
