PLATE LI. 
(Figures 1-7,13-16,18. 23-26, 28, 29, 31-41 by G. B. Simpson; 8, 9, 20-22 by J. M. Clakke; 17 by F. B. Meek; 19, 27, 
30 by E. Emmons; 10-12 copies.) 
Genus HUSTEDIA, gen. nov. 
Page 120. 
Hustedia Mormon I, Mavcou. 
Figs. 1-4. Ventral, dorsal, frontal and profile views of an average individual; showing the coarse plication 
of the surface. 
Fig. 5. An enlai-ged view of the exterior of the pedicle-valve. X 2. 
Fig. 6. The opposite side of the same specimen ; showing the coalesced deltidial plates. X 2. 
Fig. 7. An enlargemeu.1 of the umbonal region ; showing the coalesced deltidial plates, and the flattened 
cardinal slopes of the brachial valve. X 5. 
Fig. 8. A preparation of the hinge-plate, viewed from in front ; showing the elevation of the large 
recurved median part, the crui al lobes, and the projection of the anterior ligulate process. 
Fig. 9. A pi’otile view of the same specimen ; showing the great recurvature of the body of the plate, 
the direction of the crural processes, and the extent of the anterior ligulate process. X 5. (c.) 
Coal Measures. Near Kansas City, Missouri. 
Genus UNCINELLA, Waagen. 
Page 123. 
Uncinella typica, Waagen. 
Figs. 10-12. Dorsal, profile and ventral views of a typical specimen; showing the exterior characters. 
(Waagen.) 
Permo-carboniferous. Salt-Range, India. 
Genus EUMETIilA, Hall. 
Page 115. 
Eumetria Verneuiliana, Hall. 
Figs. 13, 14. Dorsal and profile views of an unusually elongate shell. 
Figs. 15, 16. Similar views of an example which has the usual form of the species. 
Fig. 17. A dorsal view of the oiiginal specimen of the species, enlarged. 
In all the above specimens the deltidial plates are seen to be wholly coalesced, which is the nor¬ 
mal condition at maturity. 
Fig. 18. A dorsal view of a small individual in which the median division-line between the deltidial plates 
is still retained. X 3. This and the preceding figure represent the s^iecies as it occur.s in the 
limestone at this locality. 
Fig. 19. The detached brachidium, enlarged, and viewed from the ventral side; showing the attachment 
of the crura to the primary lamellae, the foian of the loop, its long, straight bifurcate stem, and 
the shape of the spiral cones. X 2. (c.) 
Fig. 20. The interior of the cardinal region of articulated valves, viewed with the plane of the hinge hori¬ 
zontal. This preparation shows, in the background, the large foramen and below it the flattened 
inner surface of the coalesced deltidial plates, which afford no evidence of a median suture. On 
either side are the elongate teeth filling the equally elongate dental sockets. The hinge-plate 
consists of two parts, {a) the posterior portion which takes the form of a crescent, its horns lying 
back upon the inner surface of the deltidial 2 dates and the umbonal slopes; this is connected 
laterally with the socket-walls and anteriorly with (&), the anterior poi'tion, which is tent-shaped 
and consists of two deeji and bread lateral lamellae resting on the bottom of the valve, united 
above by a deeply concave horizontal jilate; from the anterior angles formed by the union of 
these plates arise the divergent and greatly elevated ci-ural ju-ocesses. In this figure the anterior 
portion of this ajj^iai'afais is considerably foreshoi'tened. It will be observed that the specimen 
shows no evidence of the delthyrial tube occurring in Retzia, Hustedia, etc. X 10. (c.) 
Fig. 21. The same preparation viewed with the pedicle-valve inclined upward; showing the length of the 
anterior transverse plate. X 5. 
Fig. 22. A view of the same s^iecimen with the pedicle-valve inclined downward ; showing the elevation of 
the crural plates and processes. X 5. 
St. Louis group. Spergen Hill, Indiana. 
Fig. 23. An internal cast of a brachial valve which retains a portion of the hinge-plate and shows the back¬ 
ward projection of the posterior crescent. 
Fig. 24. A dorsal view of a sjiecimen, drawn fi'om the impression of a natural mould represented in fig. 25. 
Fig. 25. A mould of the exterior of a portion of both valves. 
Fig. 26. The umbonal portion of the same specimen, enlarged ; showing the maximum development of the 
foraminal tube, which is but a slightly introverted lamina. The figure was also designed to 
represent the sepai'ation along the hinge-line of the deltidial plates from the flattened cardinal 
sui'faces of the brachial valve, but by an error in the lithography this line has been made to 
appear as a break continuous with a slight fracture on each side of the i^edicle-valve. X 3- 
St. Louis grouj). Ch’eene county, Missouri. 
