I'LATE XXXVII— Continued. 



Si'iKFFER FoKBKSi. Norwood iiiul Prattoii. 



Fi". IS. An eiilarj^etl view of the cai'dinal area of the pedicle valve, from which the siii-face layei- has been 

 partially exfoliated, exposing the vertical canals traversing- the shell-snV>stance. 

 Bnrlington limestone. BwrlingUni, Iowa. 



Spirifek lateralis. Hall. 

 See Plate 32. 

 Fi". 19. An enlargement of the caidinal area, showing features similar to tlie pre(-e(iing. 

 Warsaw group. Cli/ttm, Illinois. 



Spirifer Williamsi, sp. IIOV. 



Fio-s. 20-22. Views of an enlarged example ; showing the low, coai'.se and i^parfe plication of the median 

 fold and sinns. 



Chemung group. Allegany county, N. Y. 



SrIRIFER CaNANDAICU^, .sj). IIOV. 



Figs. 23, 24. Two views of a somewhat distorted individual ; showing the low, roniuled hiteral plications 



and narrow umbo. 

 Fig. 25. An enlargement of the surface ; showing the closely crowded concentric rows of fine grannies or 



spine-bases. X u. 



Hamilton shales. Canandaigua Lake, N. T. 



Spirifer Hungerfordi, Hall. 



Fio-a. 26, 27. Dorsal and profile views of a specimen with elongate outline and short hinge. 



Fig. 28. Anterior view of the same individual ; showing the ilevelopment of the median fold and sinus. 



Fig. 29. A shell with an extended hinge-line and short longitudinal axis; presenting the extreme of varia- 

 tion in this respect. 



Fig. 30. The central jiortion of the interior of a pedicle-valve ; showing the teeth, dental lamellie and mus- 

 cular impressions. X 2. 



Upper Devonian. Rochford, Iowa. 



Spirifer plenus, Hall. 

 See Geol. Rept. of Iowa, p. 603, pi. xiii. 1858. 

 Fig. 32. An eidargement of a poi'tion of the inner surface of the shell ; showing the puncta. X 4. 

 Fig. 38. A portion of the external surface near the anterioi' margin. X 6. 

 Burlington limestone. Burlington, Iowa. 



