230 
AUG. F. FOERSTE 
maximum diameter of the segments of the siphuncle is 13 mm. 
At its passage through the center of the septum the siphuncle is 
constricted abruptly to a diameter of 5 or 6 mm. The outer sur- 
face of the deposit which lines the inner side of the walls of the 
segments of the siphuncle is corrugated vertically. A short dis- 
tance above mid-height of the segments, these corrugations are 
interrupted by a horizontal groove. This groove marks the line 
at which deposits embracing successive septal necks meet. 
The thickness of the shell is somewhere between one-half and 
three-quarters of a millimeter. Its outer surface is striated or 
banded transversely. Along the lateral sides of the conch these 
striae are directly transverse, but along its ventral side they 
curve downward moderately, locating the hyponomic sinus. 
Locality and Horizon. — From Hartsville, Indiana, at the top 
of the Laurel limestone, immediately beneath the Waldron shale. 
Specimen No. 6056, In the Walker "^Museum at Chicago Uni- 
versity. 
Rhynchorthoceras duhium. — The type of Rhynchorthoceras 
duhium is curved at its base, but straight farther up. One of the 
lateral sides retains the surface striae, curving downward ven- 
trally. The opposite lateral side exposes the sutures of the septa. 
The conch is slightly compressed laterally, and the siphuncle is lo- 
cated ventrad of the center of the conch. A second specimen, not 
described by Hyatt, shows very well the downward curvature of 
the transverse striae along the ventral side of the conch. The op- 
posite side exposes the sutures of the septa, which are directly 
transverse. The siphuncle is seen at the top of the specimen. 
(Plate XXXV, Figs. lA, B.) 
Locality and Horizon. — Hyatt referred to his type as occur- 
ring in the Niagara group of Indiana. The exact locality is un- 
known, but it probably came from the upper part of the Laurel 
limestone in the St. Paul or Hartsville area. This type is num- 
bered 2132 in the Museum of Comparative Zoology at Harvard 
University. The second specimen is numbered 2133. 
Joliet specimen. — One specimen includes, at its base, part of 
the lengthwise curved portion. The transverse striae curve dis- 
tinctly downward on the ventral side of the conch. There is a 
tendency toward obscure transverse costae, which slope obliquely 
downward from the dorsal toward the ventral side of the conch 
at a rate much more rapid than that of the transverse striae. 
