PLATE 54. 
Page 
Figs. 1-8. Rhynchonella (Stenocisma) tethys. 835 
1-3. Dorsal, ventral and profile views of a small specimen of the species. 
4-8. Dorsal, ventral, profile, cardinal and front views of a large individual of the species. 
Figs. 9-13. Rhynchonella (Stenocisma) billingsi.. 336 
9. An enlarged dorsal view of a young individual, specimen, fig. 11. 
10. Enlarged dorsal view of another specimen. 
11-13. Ventral, profile and front views of a specimen of this species. 
Figs. 14-19. Rhynchonella (Stenocisma) Carolina. 337 
14-18. Dorsal, ventral, profile, cardinal and front views of a cast, showing the general features 
of the spedes. 
19. Front view of a less gibbous specimen. 
Figs. 20-23. Rhynchonella (Stenocisma) royana. 838 
20-23. Dorsal, ventral, profile and front views of the specimen described. 
Figs. 24-32. Rynchonella (Stenocisma) iiorseordi.. .. 339 
24. Dorsal view of a specimen of medium size, which is somewhat thickened on the margin. 
25. Front view of a smaller individual. 
2(^ 27. Dorsal and profile views of a more globose specimen. 
28-32. Dorsal, ventral, profile, cardinal and front views of a large, well formed, and charac¬ 
teristic specimen of the species. 
Figs. 33-43. Rhynchonella (Stenocisma) sappho. 340 
33.. Ventral valve of a specimen, referred with some doubt to this species. From the Upper 
Helderberg limestones. 
34, 35. Dorsal and ventral views of a medium sized individual of the species. 
36. 37. Dorsal views .of two individuals of a larger size, showing some variation in the general- 
outline of the shell 
38-42. Dorsal, ventral, profile, cardinal and front views of a large and characteristic specimen 
of the species. 
43. Front view of a still larger individual, showing a greater gibbosity. 
Figs. 44-59. Rhynchonella (Stenocisma) congregata. 341 
44, 45. .Dorsal and front views of a small globose form of the species. 
46-50. Dorsal, ventral, profile, cardinal and front views of a full grown and characteristic 
specimen. / 
51, 52. Ventral views of casts of the species, showing considerable variation in the form of the 
muscular impressious. 
53, 54. Ventral and cardinal views of a more elongated form, showing the cavities left by the 
removal of the dental lamellae and hinge-plate; also the median septum and the filling of 
the small triangular fissure in the beak of the dorsal valve. 
55. Dorsal view of a cast of this species. 
56, 57. Enlargements of the cardinal parts of the casts of dorsal valves, showing the filling 
of the rostral cavities and fissure. 
58, 59. Enlarged views of artificial casts made in the natural moulds of the dorsal valves, show¬ 
ing the hinge-plate, dental sockets, median septum and triangular fissures in different 
stages of development. 
