216 
AUG. F. FOERSTE 
length of one camera where its margin invaginates into the upper 
part of the septal neck next beneath. The lower margin of each 
septal neck extends about 1 mm. below the top of the underlying 
one. The light colored layer appears to be merely a calcareous 
inner lining of the darker colored one and, as far as known, 
also extends downward only the length of a single camera. 
The interior of both the siphuncle and of the endocone (Plate 
XXIV, Figs. 6D, E), is lined by a calcareous deposit, which 
attains a thickness of about 4 mm. at the top of the endocone, 
diminishing to 2 mm. about 3 camerae farther up, and to about 
three-quarters of a millimeter 8 camerae above the top of the 
endocone. About half way dovv^n the length of the endocone the 
calcareous deposit completely fills its interior. The matrix filling 
the upper half of the axial part of the endocone and the over- 
lying part of the siphuncle is obliquely annulated in a manner 
strictly corresponding to the annulations on the exterior of the 
siphuncle, but the annulations are less prominent. Passing 
along the axial part of the solid deposit filling the lower half of 
the endocone is a thin band, a millimeter or less in width, but 
only about one-fifth of a millimeter thick dorso-ventrally, which 
evidently was originally an endosiphuncle, filled in successively 
from above by curved transverse, thin layers whose concave sides 
face upward. 
Locality and formation. — From the cephalopod bed at the base 
of the Maquoketa on Little Calumet creek, 6 miles south of 
Louisiana, Missouri. Collected by. Ulrich and Kirk in 1911, 
and now in the U. S. National Museum. 
15. ASCOCERAS BARRANDE 
Genotype: Ascoceras bohemicum Barrande. Barrande, Syst. Sil. du 
Centre Boheme, pi. 93 
The Silurian genera Ascoceras, Glossoceras, and Aphragmites 
have laterally compressed gerontic living chambers, differing in 
this respect from the Ordovician genus Billingsites in which these 
chambers are depressed dorso-ventrally. In the three Silurian 
genera the upper part of the living chamber is contracted into a 
tubular portion which terminates in Ascoceras and Aphragmites 
in a simple transverse aperture, but which in Glossoceras has 
distinct dorsal and lateral crests, with intermediate sinuses. 
The general transverse section of the upper tubular portion may 
be circular or moderately depressed dorso-ventrally. In Ascoceras 
