FOSSILS OF THE ST. LOUIS GROUP. 543 



CEPHALOPODA. 

 NAUTILUS. 



XAUTILUS (TEMNOCHEILTJS) COXANUS, M. and W. 



PI. 23, Fig. 1. 

 yautiliw (TemnocheUus) Coxanus, MEEK and VORTHEX, 1869. Proceed. Acad. Kat. Sci., Pbila. 



SHELL rather small, sub-discoid, broadly rounded, or de- 

 pressed convex over the periphery; umbilicns wide, rather 

 deep, perforated, and showing more than three-fourths of the 

 dorso- ventral diameter of each inner turn ; volutions about 

 two and a half to three, very slightly concave along the 

 dorsal or inner side for the reception of the periphery of 

 each succeeding turn within, more or less narrowly rounded 

 (sub-angular in young specimens), and ornamented by 

 about fifteen small nodes around the middle of each side, 

 from which point the inner side rounds very abruptly into 

 the umbilicus ; septa separated on the outer or ventral side 

 by spaces one-fifth to one-sixth the transverse diameter of 

 the volutions, at the point of measurement, arching slightly 

 backward in crossing the periphery; body chamber coin- 

 posing about half of the outer volution; siphuncle small, 

 and situated sub-centrally, or somewhat nearer the outer 

 or ventral side; aperture transversely oval. Surface orna- 

 mented with distinct, regular, longitudinal, raised lines, or 

 small, revolving costse, narrower than the rounded furrows 

 between, those along the middle of the ventral or outer side 

 being smaller and more crowded than those toward the 

 lateral regions; crossing all these are numerous very fine, 

 crowded stria 1 of growth, which curve strongly backward 

 in passing over the periphery, parallel to the margins of 

 the very profound sinus in the lip on the ventral side.* 



(ireatc-st diameter of a mature specimen, 2.23 inches; 



* This would be the dorsal side, according to the nomenclature most generally ued. 



