PLATE XLV. 



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(Figures 1-3, 0-12, 16, 18-24, 26-28, by R. P. Whitfield; 4, 6, 13-16, 25, 29, 30 by E. Emmons; 17 by G. B. SIMPSON.) 



Genus ATHYRIS, McCoy. 



Page 83. 



Athyris vittata, Hiill. 



Figs. 1-3. Dorsal, profile and anteiior marginal views of a normal individual j showing its comparatively 

 short transverse diameter and the development of the median fold and sinus. 



Fig. 4. The hinge-plate as viewed from above ; showing the trilobation of the anterior mai-gin, the deep 

 depression of the median portion, the coalescence of the lateral portions with the socket-walls, 

 and the large, unobstructed visceral foramen. The lateral lobes are the bases of the crura and 

 are incorrectly represented as entire at their outer extremities. X 3. (c.) 



Fig. 5. The interior of the cardinal portion of conjoined valves, the brachial valve being above. This 

 view shows the elevation of the anteiior face of the hinge-plate, the internal opening of the 

 visceral foramen, the extension of the median lobe of the plate, the thickened crural plates, 

 the crura attached to the crural lobes and their mode of union with the primary lamellae of 

 which a portion is shown. X 3. (c.) 



Hamilton group. Falls of the Ohio. 



Athyris Cora, Hull. 



Figs. 6-10. Dorsal, profile, cardinal, ventral and frontal views of the original specimen, which is somewhat 

 exfoliated about the umbones ; showing the sublenticular contour and the low median sinus on 

 each valve. 



Hamilton gi-oup. Delphi, N. T. 



Athyris spiriferoides, Eaton. 



Fig. 11. Dorsal view of a large and senile individual, having the surface lamells highly developed and the 

 median fold conspicuously elevated at the anterior margin. 



Fig. 12. The interior of a pedicle-valve ; showing the mature condition of the foramen without deltidial 

 plates, the pedicle-, adductor and diductor scars. 



Hamilton group. Soft sluiles of Western New York. 



Fig. 13. A preparation of the brachidium, one of the spiral cones being removed to expose the structure 

 of the loop. This figure shows the depressed ventral surface of the cones, the mode of attach- 

 ment of the crura to the primary lamellse, the anterior position of the loop, its broad lateral 

 branches and saddle, the long stem, and the width and extent of the accessory lamellae. 

 X2. (c.) 



Hamilton group. Alpena, Michigan. 



Fig. 14. An enlargement of the hinge-plate ; showing its subquadrate-triangular outline, the oblique aper- 

 ture of the visceral foramen, the thickening of the crural bases and the elevation of their 

 posterior extension in the form of socket-walls ; also the dental sockets and the slight submai-- 

 ginal thickening outside of them. X 3. 



Fig. 15. An anterior view of the same specimen ; showing the stout crural plates resting upon the bottom 

 of the valve, and forming the inner wall and base of the dental sockets. In the background 

 are seen the posterior elevation of the socket-walls, the visceral foi'amen and the beak. X 3. 

 Hamilton group. Clarke county, Indiana. 



Fig. 16. A dorsal view of conjoined valves of a small individual on which the surface lamellae are few 

 and distant. 



Hamilton group. Western New York. 



Fig. 17. The inteiior of a brachial valve ; showing the structure of the articulating apparatus and the 

 elongate scar of the adductor muscles. 



Hamilton group. Falls of the Ohio. 



