294 
AUG. F. FOERSTE 
equals 57 per cent of that of the conch. The curvature of the 
septa if continued to the center would cause a maximum con- 
cavity of 5 mm. where the diameter of the conch is 46 mm., 
and the segments of the siphuncle at this point contract from a 
maximum width of 26 mm. at the annulations to scarcely 19 
mm. at the inner margin of the septal necks. The septa are 
adnate to the lower surface of the siphuncular annulations, 
becoming free from the latter along a circle 23 mm. in diameter. 
The septal necks curve downward for a distance of slightly more 
than one millimeter below the general curvature of the septae. 
The connecting rings that extend from the base of one septal 
neck to the septum next beneath form the annulations of the 
siphuncle, and in vertical sections they present strongly convex 
outlines laterally, while their upper surface curves strongly in- 
ward or even slightly downward on approaching the base of the 
septal necks. The vertical distance between consecutive siphun- 
cular annulations is from one-fifth to one-fourth of the height 
of the camerae. 
The surface of the conch is smooth or obscurely striated 
transversely with a tendency toward a slight groove at the 
sutures of the septa. 
Locality and Horizon. — From Watertown, New York; occur- 
ing in the Black River limestone. Specimen from duplicate 
material in the New York State Museum of Natural History, 
at Albany, New York; presented by Dr. Rudolf Ruedemann. 
Remarks . — Actinoceras tenuifilum centrale is distinguished from 
typical representatives of the species by the central position of 
its siphuncle; the camerae are relatively more numerous, pro- 
ducing a different outline in the segments of the siphuncle; at the 
same width of the conch, these segments do not diminish in size 
conspicuoulsy toward the upper part of the conch. Additional 
specimens may prove this form to belong to a distinct species. 
