PLATE XLV. 



(Figures 1-3, li-12, 16, 18-24, se-'-'S, by K. P. WunTiELD; 4, 5, 13-15, '2b, 211, 30 by E. Emmons; 17 by G. li. Simpson.) 



Genus ATHYRIS, McCoy. 



I'ago S3. 



Atiiykis vitt.vta, Ilall. 



Figs. 1-3. Dorsal, proiile and antiMior marfjinal viows of a normal inilividual ; showing its comparatively 

 short traiisvei'se diameter and the devL'lopment of tht; median fold and sinus. 



Fig. 4. The hinge-plate as viewed from above ; showing the ti'ilobation of the anterior margin, the deep 

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

 and the large, nnobstrncted vi.sceral foramen. The lateral lobes are the bases of the ci-nra and 

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



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

 view shows the elevation of the anterior 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 jirimary lamelLo; of 

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



Hamilton group. Falls of the Ohio. 



Atiivuis Cora, Hiill. 



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 meilian sinus on 

 each valve. 



Hamilton group. Dvlyhi, N. T. 



Athyris spirlferoides, Eaton. 



Fig. 11. Dorsal view of a large and senile individual, having the surface laraellas 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 sJiales of Wester7i New York. 



Fig. 13. A prepai'ation of the brachidium, one of the spiral cones being I'emoved to expose the structure 

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

 ment of the ci-ura to the primary lamelliB, the anterior position of the loop, its broad lateral 

 bi-anches and saddle, the long stem, and the width and extent of the accessory lamella;. 

 X 2. (c.) 



Hamilton group. Alpena, Michigan. 



Fig. 14. An enlargement of the hinge-plate ; showing its subquailrate-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 submar- 

 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 innei' wall and base of the dental sockets. In the background 

 are seen the posterior elevation of the socket-walls, the visceral foramen 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 lamell.'E are few 

 and distant. 



Hamilton group. Western New York. 



Fig. 17. The interior of a brachial valve ; showing the structure of the ai'ticulating apparatus and the 

 elongate scar of the adductor muscles. 



Hamilton gi-oup. Falls of the Ohio. 



