284 
AUG. F. FOERSTE 
16. Actinoceras tenuifilum (Hall.) 
Plate XXVIII, fig, 2; Plate XXXII, fig, 1 
Ormoceras tenuifilum Hall, Pal. New York, 1, 1847, p. 55, 
pi. 15, figs. 1, la-c] pi. 16, figs. 1, 1 a-e; pi. 17, figs: 1, la, b. 
Type specimen.- — The specimen represented by fig. 1 on plate 
15 of the publication cited above is regarded as the type of the 
species. Its apical angle is 12 degrees. According to figure la 
on plate 16, 6 camerae occupy a length equal to the diameter 
of the conch at the top of the series being counted, at the smaller 
end of this type. The siphuncle is large. According to figure 
la on plate 15, it is submarginal in position. In reply to an 
inquiry regarding the vertical striae illustrated by Hall in figure 
1 and again in figure lb on plate 15, Dr. Ruedemann states in a 
letter : 
The surface marking on specimen figure 1 is microscopic, but very 
sharp and distinct. There are about 7-10 unequal striae to 1 mm. 
Your assumption that they belong to an interior coat is probably 
right, for there is a smooth patch over them at the upper end of the 
conch. Besides these longitudinal lines there is in one place also a 
system of fine transversal lines. The latter probably belong to the 
surface and have been projected upon the lower layer when the outer 
layer was dissolved. 
Cotypes. — In the specimen represented by figure Ic on plate 
15, the apical angle is 11 or 12 degrees. Along the smaller part 
of the specimen 6.5 camerae occupy a length equal to the diame- 
ter of the conch, increasing to 7 camerae toward the larger end. 
About 90 mm. above the smaller end, the diameter of the speci- 
men is 46 mm., that of the siphuncle is 24 mm., and the latter 
is about 2 mm. from the ventral wall of the conch. The surface 
of the shell is smooth. 
In specimen lb on plate 16, the margin of the siphuncle is 
within 1 or 2 mm. of the ventral wall of the conch; 6 or 7 camerae 
occupy a length equal to the diameter of the conch. In speci- 
men Ic on the same plate the siphuncle again is submarginal, 
and the surface of the shell is smooth. The present location of 
