MARCELLUS LIMESTONES AND THEIR FAUNAS 127 



entirely preserved, this chamber has a length of 45 mm, which 

 is equal to the depth of 6.5 chambers. 



On the exterior the surface is ornamented by fine concentric 

 or horizontal imbricating or engraved lines, which are bunched 

 together into low concentric annuli and are crossed vertically 

 by ridges of about the same size. These are 10 in number, to 

 correspond with the prism angles. Where these cross the annuli, 

 they are raised into projections which appear for the most part 

 to be short, stout and blunt but in some vertical sections of the 

 shell are apparently extended, acute and spiniform. These 

 exterior markings become fainter on the body whorl, but are 

 plainly visible to the aperture, in this respect contrasting to the 

 condition of the internal surface. The aperture is sinuous wath 

 a marked channel on the left lateral margin. 



Dimensions. The specimenis observed have an apertural diame- 

 ter of 30 to 40 mm and bear 16 septa in a distance of 100 mm from 

 the last downward. The approximate entire length of these 

 shells was 250 num. 



Locality. Manlius; John D. Wilson, collector and donor. 



Macrochilina onondagaensis sp. nov. S'hell rotund with short 

 acuminate spire having incurved slopes, its length being about 

 i the entire length of the shell, or 3 that of the body whorl. 

 Whorls largely concealed. Surface convex, sutures impressed; 

 body w^horl very high, somewhat aibruptly convex near the suture 

 where the surface of the penultimate whorl is overlapped -for 4 

 of its width. Non-umbilicate but with the columellar lip well 

 defined and slightly twisted; aperture entire, outer lip but 

 slightly thickened. 



Fig. iMacrochilina onoiidagaensis natural size, Agoniatite limestone, 

 Manlius N. Y. 



