EXPLANATION OF PLATE XXVIII. 



Figs. 1-8. RHYNCHOTETRA MISSOURIENSIS n. sp p. 210 



1-5. Pedicle, brachial, lateral, posterior and anterior views of a 

 nearly perfect specimen. (W. M., No. 13962.) 6. Anterior 

 view of a specimen. (D. K. G.) 7-8. Posterior and pedicle 

 views of the specimen ground for the cross-sections of the 

 rostral portion of the shell. (W. M., No. 13965.) 

 Burlington limestone, Missouri. 



Figs. 9-12. RHYNCHOTETRA ELONGATUM n. sp p. 209 



Pedicle, brachial, lateral and anterior views of a nearly perfect 

 specimen, the holotype. (W. M., No. 8549.) 



Pierson limestone, near Springfield, Missouri. 



Figs. 13-24. TETRACAMERA SUBCUNEATA (Hall) p. 214 



13-15. Pedicle, brachial and posterior views of a very perfect speci- 

 men. 16-18. Pedicle, brachial and anterior views of another 

 specimen. 19. Brachial view of a specimen with very broad 

 plications. 20. Pedicle view of a specimen with very concave 

 postero-lateral slopes. 21-22. Brachial and lateral views of a 

 narrow, elongated specimen. 23-24. Pedicle and lateral views 

 of a very short and thick specimen. (W. M., No. 7724.) 

 Salem limestone, Salem, Indiana. 



Figs. 25-34. TETRACAMERA ARCTIROSTRATA (Swallow) p. 215 



25-29. Pedicle, brachial, lateral, anterior and posterior views of a 

 very perfect specimen. (D. K. G., No. 401.) 



Salem limestone, Boonville, Missouri. 



30-34. Similar views of another specimen. (D. K. G., No. 501.) 

 Salem limestone, Alton, Illinois. 



Figs. 35-39. TETRACAMERA MISSOURIENSIS n. sp p. 216 



35-36. Pedicle and lateral views of the internal cast of a pedicle 

 valve. 37-38. Brachial and lateral views of the internal cast 

 of a brachial valve. 39. View of the internal cast of a brachial 

 valve. Cotypes. (W. M., No. 14280.) 



Residual chert, Callaway County, Missouri. 



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