AMERICAN PALEOZOIC CEPHALOPODS 
261 
ing the form of tubes connected by short central passages of 
much smaller diameter. In form, the siphuncle closely resembles 
that of Amphicyrtoceras orcas (Hall), from the Racine of Wis- 
consin, but the conch is much more elongate. 
The surface of the shell is crossed by transverse, and rather 
faint, raised lines or striae. The surface, of the cast of the in- 
terior of the specimen is faintly ribbed vertically, as in some 
specimens of Amphicyrtoceras orcas. 
Locality and horizon. — Greenfield, Wisconsin; in the Racine 
member of the Niagaran. No. 2315, in the Museum of Compara- 
tive Zoology, at Harvard University. 
Living chambers from Wamvatosa. — With the specimen de- 
scribed above, consisting chiefly of the phragmacone, are cor- 
related two living chambers, found at another locality. These 
living chambers agree fairly well in size and cross-section with 
the remnant of the living chamber preserved in the preceding 
specimen. Moreover, these living chambers are of such length, 
and have such a slow rate of contraction toward the aperture as 
to suggest that they belong to a slowly enlarging species, and 
Amphicyrtoceras lentidilatatum is such a species. 
At the base of one of the living chambers, the dorso-ventral 
diameter is 70 mm., and the lateral diameter is 78 mm. Along 
the dorsal side of the living chamber, the margin of the aperture 
rises 78 mm. above the suture at its base. Here the lateral diam- 
eter is 69 mm., and the dorso-ventral diameter is estimated at 
63 mm. Distinct contraction of the living chamber begins about 
30 to 35 mm. above its base. At the base of the cast of the in- 
terior, there is a transverse groove 6 mm. high, locating the 
annular attachment ring following the inner wall of the chamber. 
This groove is crossed by 10 low vertical ribs in a width of 
35 mm., their upward continuations being faintly visible for 
some distance above the transverse groove. Laterally this 
groove makes an angle of 10° with a horizontal plane, sloping 
from the dorsal side downward toward the ventral. The margin 
of the aperture forms a broad shallow lobe on the ventral side ; 
it rises laterally and ventro-latdrally, and curves distinctly, 
though only moderately, downward along the median part of 
the ventral side, thus locating the hyponomic sinus. Toward 
the upper part of the living chamber, the median part of the 
ventral side extends slightly outward beyond the general trans- 
