PLATE LI. 



(Fignrea 1-7, 13-16, 18, 23-28, 28, 29, 31-41 by G. B. Simpson; 8, fl, 20-22 by J. M. Clabke; 17 by F. B. Meek; 19,27, 



30 by E. Emmons; 10-12 copies.) 



Genus HUSTEDIA, gen. nov. 



Page 1-20. 

 HuSTEDIA MORMONI, Maicou. 

 Figs. 1-4. Ventral, dorsal, frontal and profile views of an average individual ; showing the coarse plication 

 of the surface. 

 An enlarged view of the exterior of the pedicle-valve. X 2. 



The opposite side of the same specimen ; showing the coalesced deltidial plates. X 2. 

 An enlargement of the umbonal region ; showing the coalesced deltidial plates, and the flattened 



cardinal slopes of the brachial valve. X 5. 

 A preparation of the hinge-plate, viewed from in front ; showing the elevation of the large 



recui-ved median part, the crural lobes, and the pi-ojection of the antei'ior ligulate process. 

 A profile 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. 

 (Waagbn.) 



Permo-carbonifei-ouB. Salt- Range, India. 



Genus EUMETRIA, Hall. 



Page 115. 



Eumetkia Veuneuiliana, 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 original sj)ecimen 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 doi-sal 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 species as it occurs in the 

 limestone at this locality. 



Fig. 19. The detached brachidiura, enlarged, and viewed from the ventral side ; showing the attachment 

 of the crura to the primary lamellse, the form of the loop, its long, straight bifurcate stem, and 

 the shape of the spiral cones. X 2. (c.) 



Fig. 20. The inferior of the caiilinal 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 hoins lying 

 back upon the inner sui-face of the deltidial plates and the umbonal slopes ; this is connected 

 laterally with the socket-walls and anterioi-ly with (6), the anterior portion, which is tent-shaped 

 and consists of two deep and bread lateral lamellae resting on the bottom of the valve, united 

 above by a deeply concave horizontal plate ; from the anterior angles formed by the union of 

 these plates arise the divergent and greatly elevated crural processes. In this figure the anterior 

 portion of this apparatus is considerably foreshortened. It will be observed that the specimen 

 shows no evidence of the delthyrial tube occui-ring in Retzia, Hustbdia, 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 specimen with the pedicle-valve inclined downward ; showing the elevation of 

 the crural plates and processes. X 5. 



St. Louis group. Spergen Hill, Indiana. 



Fig. 33. An internal cast of a brachial valve which retains a portion of the hinge-plate and shows the back- 

 wani projection of the posterior crescent. 



Fig. 24. A dorsal view of a specimen, drawn from the impression of a natural mould represented in fig. 25. 



Fig. 25. k 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 separation along the hinge-line of the deltidial plates from the flattened cardinal 

 surfaces of the brachial valve, b it 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 pedicle-valve. X 3. 

 St. Louis group. Chreene county, Missouri. 



