280 
AUG. F. FOEKSTE 
Unfortunately the age of neither Leiirorthoceras hanseni nor 
of Leurorthoceras childleyense is fully established. In both cases 
the type specimens occur associated with other specimens of 
undoubted Black River ^ge, but in each case the Leurorthoceras 
in question consists of a matrix differing lithologically from that 
of the associated Black River fossils sufficiently to admit of the 
possibility of the former belonging to a different geological 
horizon. 
Orthoceroids with flattened ventral sides are known also from 
other localities and horizons but are not known to have the same 
structural characteristics of the siphuncle as in Leurorthoceras. 
In Orthoceras capitolinum Safford, from the Bigby member of 
the Trenton at Nashville, Tennessee, according to the figures 
presented by Safford, the lateral angles of this species are even 
more angular than those of Leurorthoceras hanseni. About 15.5 
camerae occupy a length equal to the lateral diameter of the 
conch at the top of the series of camerae being counted. At 
the base of the specimen the lateral diameter is 62 mm., the dorso- 
ventral one is 38 mm., the diameter of the siphuncle at its pas- 
sage through the septum is 15 mm., and the distance of this 
siphuncle from the ventral wall of the conch is about half a 
millimeter. It is difficult to conceive how there could be room 
here for a strongly nummuloidal siphuncle. I am informed by 
Prof. L. C. Glenn that the type of Orthoceras capitolinum 
can not be found in the Safford collection at Nashville, Tennessee, 
and probably has been lost. 
Specimens in the U. S. National Museum, identified as Actino- 
ceras capitolinum, have undoubted nummulitic siphuncles, 15 
to 20 mm. in diameter, in direct contact with the ventral wall 
of the conch, but not enough of the circumference of the conch 
is preserved to show the subtriangular cross-section. 
In Orthoceras murrayi Billings, from the Black River limestone 
on St. Joseph Island, Lake Huron, the cross-section is more 
triangular than in any of the species discussed so far. This 
triangularity is due not only to the flattening of the ventral side 
of the conch but also to the flattening of the two dorso-ventral 
sides, producing a distinct line of angularity along the median 
