472 
PALAEONTOLOGY OF NEW YORE. 
at its base, having two minute saddles, embracing the narrow, central por¬ 
tion, where the septa are coincident with the walls of the siphuncle, and 
penetrates to at least four-fifths of the depth of the adjacent air-chamber. 
Suture-lines distinctly impressed and clearly defined, but not wide; imbri¬ 
cating at the summits of the saddles and at the bottom of the lobes. 
Siphuncle small, cylindrical; its other features not determined. 
Test about .5 mm. in thickness, rarely preserved in any of the specimens. 
Surface marked by fine transverse strire, the characters not fully ascertained, 
but which make a gentle curve forward, and bend backward toward the 
periphery, often indicating the existence of a fascicular arrangement, or an 
attenuation of stronger striae, which produce the low, gentle undulations 
sometimes observable in the worn and macerated fossil, especially toward the 
umbilical margin. The sinus has not been determined. 
The internal cast is essentially smooth, with the suture-lines distinctly 
impressed, and in certain conditions of weathering these lines become more 
conspicuous from absorption or solution of the prominent portions of the 
saddles and the angular basis of the lobes. The diameter of an ordinary 
specimen is from thirty to fifty or sixty mm. The smallest specimen 
measured has a greatest diameter of thirteen mm., but the individual does 
not retain the chamber of habitation; its greatest transverse diameter is ten 
mm., showing it to be more rotund than the older specimens. The largest 
specimen measured has a lateral diameter of about 100 mm., and several 
others measure eighty to ninety mm. 
This species bears comparatively little critical resemblance to any of the 
species of the New York formations, in none of which are the volutions so rotund 
except G. plebeiformis, and in young forms of G. expansus. It has a general 
resemblance, in the direction of the septa, to G. Patersoni; but in that one the 
inner angular lobe is outside of the umbilical margin, the lateral saddle is 
narrower and more elongate, and. the outer lobe is more extended and acute, 
though holding a similar position on the volution. 
Formation and locality. In the Goniatite limestone, at Rockford, Indiana. 
