452 



Fossils of the Chazy Limestone. 



De Orbigny, and others, lc will be seen that some, such as Schizos- 

 toma delphinuloides, S.fasciatum, S. taeniatwn, S. vittatum, S. 

 costatum, Euomphalus, Dionysii, E. catillus, and other allied 

 forms, have a spiral band, with backward curving lines of growth, 

 differing only from PUurotomaria in their more slender cylindri- 

 cal whorls and wide umbilicus. Many of these, although perhaps 

 generically distinct, should, I think, at least be placed in the same 

 family with Pleurotomaria. 



Pleurotomaria docens, N. s. 



Fig. 27. 



Fig. 28. 



Fig. 29. 



Fig. 27. — Pleurotomaria docens. View of the spire of a specimen 

 from the Chazy Limestone near L'Orignal. On one 

 side the band is partly worn away or concealed. 

 28. — A portion of the band a little enlarged. 

 29. — Side view of same] specimen ; the lower part of the base 

 broken away. 



Description. — Spire nearly flat ; base sub-hemispherical ; umbi- 

 licus closed ; whorls about four, with a distinct spiral band all 

 round on the outer margin ; width, usually a little more than 

 an inch and a half; height, about two-thirds the width. 



On the upper side the whorls in the centre are gently convex 

 and elevated, so that the apex is about three lines higher than 

 the outer margin. As the whorls enlarge they gradually lose the 

 slight convexity which they possess at the centre, and become 

 more and more flattened, until at the aperture the last is either 

 quite flat or even a little concave. The first whorl is very small, 

 but 'the others somewhat rapidly enlarge so that at the aperture 

 the last one is full six lines wide, where the whole width is 

 eighteen lines. 



