Discovery of a Sessile Conularia. — Ruedemann. 159 
specimen with a length of 14.3 em. has an angle of 11°. The 
specimen illustrated rests on one edge. This, however, is not 
the common mode of compression in this species, for the 
great majority of specimens apparently show only two angu- 
lar grooves and one face of the pyramid, because the whole 
shell has been compressed into the face on which it originally 
rested. According to Holm* this mode of compression is 
found with CJonularim of quadratic section, while those of 
rhombic or rhomboidal section are compressed in the direction 
of the obtuse angles. The shell of C. gracilis Hall, which I 
have seen only strongly compressed, therefore probably had 
equal faces and a quadratic section. 
The complete flattening of the specimens without breaking, 
as well as the common bending of the proximal parts of the 
shell (pi. VIII, tig. 4), are indications of a slight flexibility of 
the shell. Hall's type also was "slightly bent or arcuate. 1 ' 
This remarkable character of C. gracilis is causally connected 
with the extreme thinness of the walls already observed by Hall. 
As the observation of small wall fragments (pi. VIII, fig. 6) 
and the abundance of smooth casts of Oonularice indicate, the 
wall was very easily destructible. This may also account for 
the frequent absence of wall remains in the young Conulariob 
while the edges are preserved. Plate VIII, figure 4, and plate 
IX, figure 5, well illustrate this breaking out or dissolving of 
the walls between the edges in even larger individuals. 
The sculpture consists of "sharp, undulating, transverse 
stria- and scarcely conspicuous longitudinal ones." (PI. IX, 
figs. 5 and 6.) The finer longitudinal ribs alone, however, are 
continuous and the wavy cross ribs connect with them. Al- 
though the latter sometimes unite to continuous and ver\- 
prominent cross bands, their whole appearance is such as to 
suggest that they are wrinkles of shrinkage. The undulating 
transverse and the finer straight longitudinal ribs. -ire so char- 
acteristic a feature that they can safely be used to distin- 
guish this form from Conularia trentonensis Hall, C. hudsoni 
Emmons and C. <in<i<lf<ihi Walcott, which have straight and 
continuous transverse ribs. The undulating transverse ribs 
are of special importance in the study of the young Conu- 
*Sveriges Kambrisk-Siluriska Hyolithidse oeh Conulariidae : Sveriges 
Geol. Unclersokning, Ser. C, No. 112. 
