PLATE 10. 



Page 

 Figs. 1-26. StREPTORHYNCHUS CHEMUNUENSI8 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 striaj are 

 bifurcate, and in their partially preserved condition, arc unequal at the margin of the 

 shell ; a few finer ones between the larger reaching half or two- thirds the way t.o 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 uusymmetrlcal. 

 8. A cast of the same valve showing the muscular impression. 

 4. The exterior of a dorsal valve which is regularly convex; the strise are sliarply elevated and 



fasciculate, there beiug two or three fluer ones between the stronger and more elevated oMs. 

 6. 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 tpwards the beak they are all sub-equal. This is the origi- 

 nal of Strophomena pectinacea. 

 6 o. An enlargement of striie, from specimen fig. 6, S. pectinacea. 



7. A convex dorsal valve with the cardinal extremities slightly rounded; the stria; 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 strise is precisely similar to those of 

 the Corniferous limestone specimens of S. pandora. 



11. A dorsal view in which the striae are sharp and sub-equal ; of the type of Stropkomtna arcto- 



itriata. 



12. A specimen of similar character which is extremely unsymmetrical. 



12 a. An enlargement of the strite which characterize the specimens like those from 11 to 17. 



J3. A ventral view of an unsymmetrical specimen. • 



14. A cardinal view of the preceding specimen. 



^6. A proQle of the same. 



16. A car4iQal view of specimen when the apex is less extended. 



}7. A profile of flg, 16. The specimens 11 to 17, are of the type of Strophomena arctottriata, 



showing various degrees of distortion. 

 J8. A ventral valve with rather deep and coarse strise. 

 ^9, 20. Cast» of (jlorsul valve« of nearly symmetrical forms. 

 <21, 22. Casts of ventral valves, 



28. k cardinal view of a cast of a large ventral valve which is symmetrical on the hinge line. 

 ^\. The cardinal profess froD) a gutta-percba cast from specimen fig. 9. 



