PT.ATK V I!— CoiitiliuLMl. 



HETEKORTHIS, nom. nov. 



Page io-2. . 

 OuTHis Clytie, Hall. 



Fig-. 20. A view iil' thi! briicliial valve of the type-specimen; showing the ai'ea and foramen of the pedicle- 



val ve. 

 Fii'. 21. The interior of a pedicle-valve ; showing; the elong-ate scars of the cai-dinal muscles and the small 



adductor impressions. 

 Fig. 22. The interior of the brachial valve. The cardinal process is simple, but veiy high, and the crui-al 



plates are much elevated, terminating abi-uptly. Muscular area small and obscurely (juadri- 



pai'tite. 

 Fig. 23. The articular area of the same valve ; showing the divisions of the muscular area. X 2. 

 Fig. 24. The surface ornamentation, consisting of a fasciculate grouping of the radiating strise, crossed by 



minute concentric lines. X 4. 



Trenton horizon. Near Frankfort. Ky. 



DALMANELLA, nom. nov. 



Page iOS. 



Okthis Evadne, Billings. 



Fig. 25. A view of the brac-hial valve of the type-specimen ; showing area and foramen of opposite valve. 

 Fig. 26. The opposite side of the same specimen. 



•' Point, Levis ; in the upper part of Limestone No. 2, Quebec group. ^' 



Orthis testudinaria, Diilniaii. 



Figs. 27, 28, 29. Three views of a small form which may prove to be a jierinanent variety of the species. 

 Fig. 30. The interior of the pedicle-valve of the same form. 

 Fig. 31. The intenor of the brachial valve. X 2. 



Trenton horizon. Mitieral Point, Wiscoiisln. 

 Fig. 32. The extei-ior of the pedide-v.alve of a normal individual. 

 Fig. 33. The exterior of the brachial valve of a somewhat larger specimen. 

 Fig. 34. A profile of the same. 



Fig. 3.5. The interior of a pedicle-valve ; showing the chai-acter of the muscular area. 

 Fig. 36. The interior of a brachial valve, retaining the articulating apophyses and the subdivision of the 



muscidar area. 

 Fig. 37. The central cardinal portion of a similar valve, enlarged to show with greater distinctness the 

 sti'ucture of the articulating aparatus. 



Hudson River group. Cincinnati, Ohio. 

 Fig. 38. The interior of a large pedicle-valve. 



Ti-enton limestone. Middleinlle, N. Y. 

 Fig. 39. The interior of a brachial valve. X 2. 



Ti-enton limestone. Lowville, N. T. 



