SUPPLEMENT. 
DESCRIPTIONS OF SPECIES FROM THE UTICA SLATE, INTRODUCED 
FOR COMPARISON AND ILLUSTRATION. 
GRAPTOLITHUS FLACCIDUS, Hall. (a. s.) 
Plate II, figures 17-19. 
Description.—Frond consisting of two slender linear flexuous stipes, 
which are widely divergent from a small short obtuse radicle. The stipes 
at their origin are gently ascending, and then curve broadly backwards 
or downwards, and maintain throughout their entire length a curvilinear 
direction ; stipes cylindrical near the base, and flattened in their exten- 
sion. Surface smooth, or with striz: so fine as to be invisible under an 
ordinary lens. The diameter of the stipe varies from two hundredths near 
its origin, to four hundredths of an inch in the fully-developed parts, main- 
taining this width to the extremity: more than one half of the width is 
occupied by the common body. ‘Test comparatively thick. Cellules nar- 
row ; from twenty-eight to thirty and near the base sometimes thirty-two 
in the space of an inch; inclined at an angle of 20° or less to the direc- 
tion of the axis. Point of the denticle or aperture obtusely rounded, 
very rarely angular: cellules free throughout their entire length. 
This is a very distinct and well-marked species, with slender lax stipes 
extending four or five inches or more from the radicle. It occurs in large 
