PLATE X. 



Platyostoma linkata. 



P»ge «1. 

 Rjr. 1. A Rinall putiilnse Bpecimen. From the UpjHM- Holilerberg' group, Onondag'a oounty. 

 Fijr- 2. The ajH-rtiiii- and »piit> <if a symmeti-ical specimen, havinjf the normal characters of the sjiecies. 

 Figs. 3, 4. Summit of the sjiiiv an<l hileral view of the sj>erimen tig'. 2. 

 Figs. S, 6. The spire and a]>erture of a larger specimen, diffei-ing fi-om the precetUng in the curving of the 



columella. 

 Pig. 7. The spii* of a specimen of medium size, which, during a part of its growth, has possessf^r] a slit in 

 the outer lip, occurring, apjiai-ently, from some at-ciilental cause, at the comnienc'enient ( f the 

 outer volution, and afterwnrds becoming closed, has left the surface plicated and ii-regular. 

 Upi>er Helilerl)erg group. S<-h(>harie, N. Y. 

 Fig. 8. The spii-e of a large individual of the ordinai-y foi-m of the species, as it occurs in the limestone. 

 Fig. 9. A sinular view of a more i-obust individual. 

 Fig. 10. Lateral view of the outer volution of a specimen similar to figure 9. 



These specimens, with two exceptions, are fi-om the Upper Helderberg limestone at Williams- 

 ville, N. Y. ; they preserve, in a well-mai ked manner, the concentric and radiating striae. 

 Fig. 11. The spire of a specimen somewhat similar to fig. 7. 



Fig. 12. Enlargement of the surface striae of the same. Hamilton shales, near Geneseo, N. Y. 

 Figs. 13, 14. Two views of a specimen, preserving the surface in great peifection. The specimen is slightly 



ilejiressed frem accidental causes. From the Hamilton shales, Canandaigua Lake. 

 Pig. 15. Enlargement of the surface of the preceding. 



Figs. 16-18. Three views of a large specimen, pi-eserving the form of the aperture and peristome. The 

 aperture is slightly rhomboidal, varying somewhat fi-om the prevailing type. From the Ham- 

 ilton shales at Canandaigua Lake. 

 Fig. 19. An unusually large individual, which presen-es the striae of gi-owth very distinctly, while the con- 

 centric striae are obsolete. Corniferous limestone, Dai-ien, N. Y. 

 Figs. 20, 21. Two views of an internal cast of the same species. Chemung group. 



Platyostoma lineata var. callosa. 



Page 23. 

 Fig. 22. The aperture of a specimen which has the appearance of P. lineata, but with a thickened callus on 



the inner lip. 

 Fig. 33. The spire of the same specimen. 



Platyostoma depiodeata. 



Piige 24. 

 Kg. 24. The apertural side of the specimen of which the outer volution has been crushed. 



Platyostoma lineata var. a.mpla. 



Page .!3. 

 Fig. 2:>. The spire. 



Fig. 26. The ajMjrtural side, showing the great elevation, large aperture and peculiarity of the columella, 

 approaching in character to Strophostylus. 



Platyostoma EnoMpHALoiDES. 



PageXS. 

 Fig.'27. Dorsal \new of the specimen. Hamilton gi'oup, York, Livingston county, N. Y. 

 Fig. 28. The base of the specimen, showing the ai>e^"ture and the cohimellar lip modified by the preceding 



volution. 

 Fig. 29. The spire as seen from above, showing the depressed upper surface of the outer volution. 



