TLATK V It— ConliiiUL'iI, 



HETEKORTHIS, nom. nov. 



I';itre iW. . 



OiiTHi.s Clytie, Hall. 



Fig. 20. A \new of the brachial valve of the type-specimen; showing- the ai-ea and foramen of the pedicle- 

 valve. 



Fig. 21. The interior of a pedicle-valve ; showing' the elongate scars of the cardinal muscles and the small 

 adductor impressions. 



Fig. 22. The intei-ior of the brachial valve. The cardinal process is simple, but very high, and the crural 

 plates are much elevated, tei-minating abi'uptly. Muscular area small and obscurely quaiiri- 

 partite. 



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



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

 minute concentric lines. X 4. 



Trenton horizon. Near Frankfort, Ky. 



DA LM AN ELLA, nom. nov. 



I'ilgc 200. 



Oktiiis Evadne. Billing.s. 



Fig. 2"). A view of the brachial valve of the type-specimen ; showing area and Ibrauien of opposite valve. 

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



"Point Levis; in the upper j^art of Limestone No. 2, Quebec gro^ip." 



Fig. 37 



Fig. 

 Fig. 



Orthis TESTuniNARiA, Daliuaii. 



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

 The interior of the jiedicle-valve of the same form. 

 The interior of the brachial valve. X 2. 



Trenton horizon. Mineral Point, Wiscojtsin. 

 The exterior of the pedicle-s'.alve of a normal individual. 

 The exterior of the bi'achial vahe of a somewhat lai'ger specimen. 

 A profile of the same. 



The interior of a pedicle-valve ; showing the character of the muscular area. 

 The interior of a brachial valve, retaining the articulating apophy.'ses and the subdivision of the 



muscular area. 

 The central cardinal portion of a similar valve, enlai-ged to show with greater distinctness the 

 structure of the articulating aparatns. 



Hudson River gi'oup. Cincinnati, Ohio. 

 The interior of a large pedicle-valve. 



Ti-enton limestone. Middleriille, N. Y. 

 The interioi' of a brachial valve. X 2. 



Trenton limestone. LovyviUe, N. T. 



