AMERICAN PALEOZOIC CEPHALOPODS 
227 
the long and short diameter of the section is as 100 to 85. A 
specimen five inches long is one inch three lines Avide at the large 
end, and two lines wide at the apex, the dilated part of the siphon 
at the latter point equalling the whole diameter of the shell, but 
being only 5 lines wide at the anterior (upper) end, where two 
chambers occupy a space of slightly less than half an inch, while 
six chambers occupy the same space at the smaller end. The 
internal structure is that of Actinoceras Stokes, though it is 
marginal in position, and the septa are more oblique.’' 
McCoy evidently had not a very clear idea as to the limits of his 
genus Uoxoceras. This is shown by the fact that the species de- 
scribed third under Loxoceras, namely Loxoceras incomitatum 
McCoy, does not have the strongly oblique sutures. His fourth 
species was Orthoceras laterale Philips. The longitudinal view 
presented in Figure 3 accompanying the original description of 
the genus is regarded here as a diagrammatic representation of 
his species Loxoceras distans, while the small cross-section is in- 
tended to show the course of the sutures in Orthoceras breynii, 
the siphuncle of the latter being located along the middle of that 
broad side along the median line of which the sutures curve mod- 
erately downward. 
26. SACTOCERAS HYATT 
Genotype: Orthoceras richteri Barrande. Syst. Sil. du Centre Boheme, 
pis. 318, 349 
Orthoceracones with relatively small siphuncles, the segments 
of the latter nearly spherical or slightly elongated. Septal necks 
short, enveloped on the interior of the siphuncle by lunate cal- 
careous deposits, which enlarge as in other Actinoceroids. Su- 
tures of the septa directly transverse. Described from the Si- 
lurian. 
It is doubtful whether the Carboniferous species Loxoceras 
distans is to be regarded as congeneric with Sactoceras. Using 
the former as the type of Loxoceras, there appears to be use for 
Sactoceras as the designation of a distinct group, certainly pres- 
ent in the Silurian, and apparently beginning with forms in the 
Ordovician in which calcareous deposits of an Actinoceroid na- 
ture are unknown. 
