Fossils of t/ie Chazy Limestone. 449 



In some of these forms which have a very sharp outer angle, 

 the band is situated exactly on the edge of the whorl, and it is 

 then smooth in all the species in which I have been able to see it 

 distinctly. In P. calyx it is double, or composed of a minute 

 flat smooth band on the upper surface sloping downwards to the 

 edge, and a similar one below sloping upwards, the two consist- 

 ing what may be called a bevelled edge to the whorl. In none 

 have I seen the striae passing over the edge of the whorl ; but it 

 is evident that as they curve backwards both on the upper and 

 under sides on approaching the edge, they must either pass over 

 it or not ; and in the latter case the band must be smooth, while 

 in the former it must consist of a simple angular bend in the 

 lines of growth. In several (and among these P. docens) the 

 band is altogether on the upper surface, but close to the outer 

 edge. Of Scaliies angulatus we have no specimens, but, ac- 

 cording to Professor Hall's description, the surface is, on the 

 u upper side of the whorls, marked by striae directed obliquely 

 backwards, and which, on passing over the angle, are directed 

 somewhat spirally forwards."* As these striae indicate the form 

 of the aperture, there must be a notch in the lip of S. angulatus, 

 with the deepest point exactly at the angle of the whorl, and 

 also an angular bend in the lines of growth equiva'ent to a band. 

 So far, then, as the presence or absence of a band and notch can 

 affect the question, there is no generic difference between Scaliies 

 and Pleurotornaria, and if the two genera are to be maintained 

 as distinct, it must be upon some other characters not yet pointed 

 out. 



It might be thought that the difference between the forms of 

 the Lower Silurian species and those of the more recent rocks 

 would be sufficient to warrant their separation into two or more 

 genera. But upon examination it will be seen that Pleuroto- 

 maria consists of more than 400 species, varying from pyramidal 

 forms, or those with an elevated and pointed spire and flat base, 

 through those that are nearly globose or with the base as greatly 

 produced as the spire, to such as P. docens, with the spire nearly 

 flat and the base conical. P. Bamsayi, which has a flat or 

 slightly concave base, represents the pyramidal form in our rocks 

 and P. docens the opposite extreme. P. Ramsayi is all spire 

 and no base, while P. docens is all base and no spire. If a plane 



• Palaeont. N. Y., Vol. I. p. 27. 

 Canadian Nat. 4 Vol. IV. No. 6. 



