PLATE 34. 



Fig. 1-6. Rhynchonella? bialveata. 233 



1 a, b. Dorsal and ventral views of a small individual. 



2 a, b, c. Dorsal, ventral, and profile views of a less elongate fc.rin. 



8 a, b, c. An individual having the plications nearly equal, and showing scarcely any indica- 

 tion of a sinus in front. 



4. An enlarged figure of the same species. 



5 o, 6, c, & 6 a, b, c. BuYijcuoKELL.t semiplicata? 

 The forms here figured closely resemble the R. semiplicata of the Pcutanicrus limestone; being a 

 little more rotund, and deeply sinuate. This form is extremely rare in the shaly limestone of the 

 Lower Ilelderberg group. 



Fig. 7 & 8. Rhynchonella inutilis. 233 



7 a, b. Ventral and profile views of a small individual. 



8 a, b. Ventral and front views of a more rotund form. 



Fig. 9 - 19. Rhynchonella transversa. 234 



9 - 14 a, b, c. A series of individuals showing a regular gradation in size, with a gradually 

 increasing depth of sinus. 



15 & 16 o, b, c. Individuals having a more strongly defined sinus and me.sial lobe; a single 

 individual having but two folds in the sinus. 



17 - 19 a, b. Rhynchonella transversa? var. 



These forms present some differences of character from those referred to tlie species proper; being 



somewhat more circular, and the lateral plications a little curving. 



Fig. 20 & 21. Rhynchonella rudis. 235 



20 a, b, c. Ventral, front and profile views. 



21 a, b. Profile and front view of a similar form, which varies in some respects. 



Fig. 22. Rhynchonella planoconvexa. 235 



22. A cast of the dorsal valve, preserving the shell upon the margin. 



