PLATE XXXI A. 



Styliola fissceella. 



Page 178. 



Tig. X. A fragment of slate with numerous crushed specimens of the fossil, enlarg-ed to three diametei-s. 



Figs. 3-t5. Individuals from the surface of the slate, showing the variety of form and surfiicc-markinffs ; 

 6g. 2 being strongly striate longituilinuUy ; tig. '^ showing transverse and longitudinal stria; ; 

 and fig. 4 pi-eserving only transvei-se striie ; while figs. 5 and Ij ai-e without visible stria; imder 

 an or»linai-y lens. All the preceding figures are from the Marcellus shale. Figs. 2-6 are 

 enlai-ged to six diametei-s. 



Fig. 7. A fragment of the Genesee slate covered with Styliola fissurella, enlarged to three diametera. 

 All the following figures are enlarged to six diameters unless otherwise indicated. 



Fig. 8. A crushed specimen showing obscure ti'ansverae striae ; the apex acute. 



Fig. 9. A crushed sj>ecimen without visible transverse strite, and with the extremity bulbiform. 



Fig. 10. A specimen in its natural proj«)rtions, the margin of the aperture broken away on one side. The 

 surface is obscurely marked by ti-ansvei-se stria;, and the extremity slightly bulbiform. 



Fig. 11. An individual which is apparently contracted near the aperture, vnth the surface faintly striate 

 concentrically, and the apex acute. 



Fig. 12. A smaller form similar to the preceding, without visible t.ransvei-se striae. 



Fig. 13. A larger compressed specimen with obscure transvei-se sti-iie. 



Fig. 14. A jwrtion of an individual where the transverse strise are more closely arranged, and more con- 

 spicuous. 



Fig. 15. An individual of large size, where the lower part of the tube is essentially smooth, or preserving 

 only obscure concentric striie, while towards the aperture these striie become much stronger, 

 and are cancellated by longitudinal stria;; the latter being visible only so far as shown in the 

 figure. All the figures from 11-15 inclusive have no perceptible expansion at the apex. 



Fig. 16, o, 6, c. Specimens showing an apparently intermittent mode of growth. 



Fig. 17. A specimen showing the insertion of one individual within another ; the outer broken margin 

 being of the shell, and the intermediate portion the filling of mineral matter between the two. 

 It is prebable that some of the iiregular specimens referi-ed to intermittent growth may be due 

 to conditions similar to fig. 17 ; but in other examples it is clearly the mode of growth. 



Figs. 18, 19. Two small individuals of regular form and acute apices, with faint, ti-ansvei-se undulations, 

 which are scareely defined as strise. 



Fig. 20. Three individuals lying in juxtaposition and preserving their natui-al propoi-tions ; two of them 

 show evidence of intermittent growth, and are contracted near the aperture, while the third one 

 is simple. The surfaces are marked by faint undulations or obsolete strife. 



Fig. 21. A short, broad form, the breadth increased by compression. 



Fig. 22. A short, broad specimen with the aperture entire. From the Genesee slate. Lexlnyton, Indiana. 



Figs. 23, 24. Two individuals of slightly different shape (fig. 23 being a Utile more compressed), both of 

 which have the sui'face distinctly cancellated by fine, longitudinal and transvei-se stiiae. 

 Fig. 24 is slightly bulbiform at the extremity, while fig. 23 is acute. 



Kg. 25. A fragment showing the cleavage surface of a calcareous layei- in the Genesee slate, which is 

 chiefly composed of Sttliola with a few Tbntaculitbs. Natural size. Cayuga creek, Erie 

 county, N. Y. 



Fig. 25 a. A polished, translucent section from a calcareous layer in the Marcellus shale, showing the trans- 

 verse and longitudinal sections of Sttliola ; enlarged to three diameters. Cherry Valley, N. Y- 



Figs. 26, 27 and 28 are very minute, slender forms of Sttliola enlarged to six diameters, as in the preceding 

 and following figui-es of this species. The apices are slii^htly bulbiform ; and on figure 27 

 there are obsolescent stria;, while figures 26 and 28 are smooth. From the compact layer 

 composed of the shells of Styliola, in the Genesee slate. Cayuga creek, Erie loanty, N. Y. 



The figures from 7 t<i 28 inclusive, except 25 o, are from the Genesee slate. The figures 29 

 and 30, and 83-36, are from the shales in the lower part of the Hamilton group, above the 

 Mai-cellus shale. 



