PLATE 9. 



Page 

 Figs. 1 - 12. StREPTORHYNCHUS CHEMUNGEN8I8 var. ARCT08TRTATA 71 



I, 2. Ventral valves of young specimens where the beaks are somewhat distorted, and the strite 



not alternating in strength. 



8, 4. External and internal views of a dorsiil valve of similar ch.iracter. 



6. Interior of a dorsal valve, the strise of which arc sharp and equal in size. 



6, 7. Exterior and interior of a larger dorsal valve, the strite of which are distinctly alternating 

 in strength. 



8. 9. Ventral and dorsal valves of a semicircular form, where the strise are sharp and of equal 

 strength. Original of Orthisina [S.] arctostriata, 13th Report on State Cabinet. 



10. Cardinal view of specimen, fig. 2, showing the distortion of the beak and the covered fora- 

 men; enlarged to two diameters. 



II. Interior of a ventral valve of a specimen having equal striaci showing muscular impression, 



teeth and covered deltidium. 

 12. Enlarged view of a cast of a specimen having sharp equal stria;, and showing the imprint of 



the adductor and retractor muscles very well preserved. 

 12. t Enlargement of surface strlse, showing their alternating character. 



Figs. 13 - 17, 26. Streptorhynohtjs chemungensis var. perversa 72 



18, 14. Dorsal valves of specimens, showing the alternating character of the strise. 



15. View of an imperfect ventral valve. 



16. Ventral valve of an individual retaining but a portion of the shell. 



17. Cast of a large dorsal valve showing the impression of the alternating slrise. 



26. View of a very convex finely striated dorsal valve; referred with doubt to S. perverta. 



Figs. 18-25,27. Streptorhynchus chbmunqensis var. pandora 68 



18, 19, 20 Dorsal and ventral views and profile of a very symmetrical specimen of the species. 

 21. Interior of a dorsal valve, showing the muscular impressions, cardinal process and socket 

 plates. 



23. Interior of a ventral valve, showing muscular impressions, cardinal area and teeth. 



24, 25. Casts of a dorsal and ventral valve, showing the characters of the muscular impressions, 



27. Exterior of a large ventral valve. 



