PLATE XXIII. 



PA OF. 



Pig. 1 . Pteeotoobinus chestebensis, M. and W 292 



1 it. View of a specimen with arms attached (somewhat flattened by pres- 

 sure), showing base. 



1 6, Anterior view of the body, consisting of the basal and first and second 

 radial pieces, together with the secondary radial and first brachial 

 pieces. 

 Anal view of the same, without the arms. 



Ptekotoceinus orassus, M. and W 290 



Specimen with the arms attached, showing the base and posterior side. 

 Posterior side view of the body of same, without the arms. 



AeohvEocidaeis muoronatus, M. and W 295 



One of the primary spines, natural size. 

 Enlargement of the fine surface striae of the same. 

 One of the interambulacral plates. 



Pbodtictcs paevus, M. and W i 297 



Profile view. 



Section showing the curve of the two valves. 



View of dorsal side. 



Ventral view. 



Enlarged surface markings. 



SPIEIFEE GLABEB var. COUTBA0TTJ8, M. and W 298 



Dorsal view, showing foramen and very small area. 

 Profile lateral view. 



Schizodtjs chestebensis, M. and W 301 



Anterior view of a cast, showing the anterior muscular impressions. 

 Lateral view of the same. 



Myalina angulata, M. and W 300 



7 (7. Anterior view, showing the broad, flattened surface formed by the in- 

 flection of the anterior margins of the valves. 

 i b. Side view. 





1 c. 



Fig. 



2. 





■1 a. 





2 b. 



Fig. 



3. 





3 a. 





3 b. 





3 e. 



Fig. 



4. 





4 O. 





4 b. 





4 c. 





4 d. 





4 e. 



Fig. 



5. 





5 a. 





5 b. 



Fig. 



6. 





C a. 





C b. 



Fig. 



i. 



