NO. 1908. NEW SILURIAN MOLLUSCA FROM MAINE— WILLIAMS. 397 



centric ridges, as shown in figure 13. On the specimens examined 

 there is no constancy in expression of these ridges, and when present 

 there seems to be no uniformity for the several whorls of the same 

 shell. It is evident from the above that the characters upon which 

 the four species are discriminated are quite inconstant. 



EXPLANATION OF PLATES. 



Plate 49. 

 Eurymyella shaleri Williams. 



Fig. 1. A right valve, natural size, not crushed. Shackford Head, Moose Island; 

 collected by II. S. Williams. 



2. A left valve, retaining the shell, crushed, natural size. Salt Works, Eastport; 



collected by N. S. Shaler. 



3. A left valve, not much crushed, natural size. Salt Works, Eastport; collected 



by N. S. Shaler. 



4. A right valve, natural size. On the east side of Seward Neck, near north 



Lubec landing, in thin bedded gray shale sandstone; collected by C. L. 

 Breger. 



Eurymyella shaleri, var. breva Williams. 

 Fig. 5. A left valve, natural size. 



6. A right valve, natural size. 



7. A small left valve, natural size. Salt Works, Eastport; collected by N. S. 



Shaler. 



Eurymyella shaleri, var. longa Williams. 



Fig. 8. A left valve, natural size. East side of Seward Neck, near north Lubec land- 

 ing; collected by C. L. Breger. 



Eurymyella shaleri, var. minor Williams. 



Fig. 9. A left valve, natural size. West side of Pleasant Point, Perry Township; 

 collected by C. L. Breger: 



Eurymyella angularis Williams. 

 Fig. 10. A left valve, natural size. 



11. A right valve, natural size. East side Seward Neck; collected by C. L. 

 Breger. 



Eurymyella? simulans WilUams. 

 Fig. 12. A right valve, natural size. 



13. A right valve, natural size. East side Seward Neck; collected by C. L. 

 Breger. 



Eurymyella plana Williams. 



Fig. 14. A left valve, natural size. East side Seward Neck; collected by C. L. Breger. 



Eurymyella recta Williams. 



Fig. 15. A left valve, natural size, figure made from wax impression of the originaL 

 East side Seward Neck; collected by C. L. Breger. 



Plate 50. 

 Figures 8, 9, 12, 13 are magnified 2 diameters, all the others natural size. 

 CHopteria hicostata Williams. 



Fig. 1. Cardinal view of right valve, showing overarching beak and high flat area. 

 2. A right valve, showing the characteristic ridges on the anterior slope; the 



same specimen as fig. 1. 

 7. A left valve, showing the deep sulcus and single fold outside on the anterior 

 slope. Specimens 1, 2, and 7, from limestone band, on the north shore of 

 Youngs Cove, Pembroke, Washington County, Maine. Collected by C. L. 

 Breger. 



