PLATE 28 B. 



Fig. 1 a - d. NucLEOsPiRA pisiformis. 



Orihis pUum : Pal. New-York, Vol.ii, p. 250. This species proves, on examination, to belong to the 

 (ienus NucLKOspiRA. It is a smaller species than tliat of the Lower Ilolderberg rocks, while it is larger and 

 more gibbous than the N. concentrica. 



1 a, b. Dorsal and ventral views of a specimen, natural size. 



1 c. Profile view of tlie same. 



1 d. An enlargement of the surface. 



Page 

 Fig. 2-9. NuCLEOSPIRA VENTRICOSA. 220 



• 2 a, b, c. Illustrations of a form having the beak more elevated than usual. 



3 c, d. An individual preserving the remains of the fine hair-like spines which cover the sur- 

 face of perfect specimens; and an enlargement of the same. 



i a, b. A cast of the interior. 



5. The interior of a ventral valve preserving the internal spires, enlarged to three diameters. 

 G a. The dorsal valve, showing the extended cardinal process and the longitudinal septum. 

 6 b. Profile of the same. 



6 c, d. Enlargement of the preceding figures. 



7 a, b. Interior of the ventral valve, and profile view of the same : enlarged figures. 



8. Interior, showing the articulation of the valves : t, t, the cardinal teeth; /, the cardinal 



process; B, B, the brachial processes. 



9. Diagram showing a longitudinal section of the valves, the articulating teeth, the cardinal 



process, spire, and longitudinal septa s, s. 



9 a. An enlarged view of the interior of the dorsal valve, showing the crura, the bases of the 

 arms for half a turn, and the connecting process which ascends from the dorsal side to- 

 wards the centre of the spire as shown in fig. 9. 



Fig. 10 - 15. NiTCLEOSPIRA ELEGANS. 222 



10 a, b. Dorsal and ventral views of a very symmetrical specimen of the ordinary size, showing 

 slight indications of the central flattening or depression. 



10 d. Profile view. 



11 a. Dorsal view of a specimen which is proportionally broader. 



12 c. Dorsal view of a specimen without mesial depression, and showing an extension in front. 



13 a, b. Dorsal and front views of a large individual which is proportionally very broad and 



deeply depressed in front. 



13 C; and 17 i ( by error for 13 d ) . Dorsal and ventral views of a gibbous specimen, which is 



produced in front. 

 14. Ventral valve, showing the spire on one side displaced. 



Fig. 16 - 19. NuCLEOSPIRA CONCENTRICA. 223 



16 a, b, c. Dorsal, ventral and profile views of a small individual, from which the pilose covering 



has been removed. 

 10 d, (. Enlargement of the dorsal and ventral sides, showing more distinctly the subrhomboi- 



dal form and the concentric laminiB of growth. The perforation of the beak appears to 



have been somewhat enlarged by fractur.e, but this feature is conspicuous in all the 



specimens of this species. 



18. Dorsal view of a specimen, natural size. 



19. A transverse section of a specimen, showing the internal spires. 



