160 
The American Geologist. 
March, 1896 
larim , as they are easily recognized by their characteristic 
form whenever the surface film is sufficiently preserved, how¬ 
ever delicate it sometimes may be. 
The cast of the interior often shows, in different parts of 
the same specimen, either the filling of the transverse ribs as 
similar ridges, or pustules (cf. pi. VIII, fig. 1), and deep fur¬ 
rows in place of the longitudinal r bs, or only -the latter; or 
in many places the cast is perfectly smooth. The last fact is 
accounted for by specimens similar to that represented in 
plate VIII, figure 4. This interesting young Oonularid. which 
at the distal end shows the straight sulcate edges of a Conu- 
laria , has in the middle part preserved the wall which con¬ 
sists of two layers,—an exterior deep black, apparently car¬ 
bonaceous one, which shows the characteristic ribs of C. gra¬ 
cilis , and a much stronger inner layer which has a more gray¬ 
ish, mineral appearance and is probably richer in calcium 
phosphate. This second layer in the middle part between the 
two upper grooves, where it is apparently least crushed, is 
almost smooth with only an obscure indication of transverse 
lines of fracture. On the sides it is broken into transverse 
ring segments. Although it is thicker than the outer layer, it 
is more frequently lost, leaving, however, a smooth cast. 
The segmental line appears as a shallow groove, scarcely 
conspicuous in most specimens. It therefore is of no help in 
identifying the young Conulariat. Of greater importance in 
this regard is the structure of the grooves at the edges of the 
pyramid, as this is generally the best preserved part of the 
fossil. In the specimens, for instance, represented in plate 
VIII, figure 4. and plate IX, figure 5. the side walls of the 
grooves alone are preserved in the distal part, the connecting 
wall being either dissolved, as indicated by the smooth sur¬ 
face between the edges in plate VIII, figure 4, or broken away 
as in plate IX, figure 5. The walls of the grooves are much 
thickened, this strengthening extending also to the adjoining 
parts of the faces, so that the grooves are lined by two thick 
ridges. The connection between fragile thin faces and stout 
edges seems to be found in other species also. Conularia lin- 
narssoni Holm* f. i. is described as having the grooves stronger 
than the segmental line and being fragile toward the aperture. 
*Op. cit., p. 130, pi. iv, figs.38-40. 
