GRAPTOLITES. ING 
and to the apex they are inclined towards the axis in opposite directions. 
These spines are sometimes on the outer margin of each mesh, and some- 
times visible only on every third one. With these rows of meshes, when 
preserved, the stipe has the appearance of a flattened corneous film with a 
central axis, which is divided into cellules as in other forms of Graptolitide ; 
and when the outer meshes are broken off, these cell-divisions project as 
mucronate points beyond the margin of the stipe. These marginal meshes 
correspond to the divisions of the stipe marked by the cell-partitions, and 
might be regarded as showing the limits of the cell-apertures, which have 
opened obliquely tc the transverse direction of the stipe. These meshes 
or cellules are arranged in the proportion of about twenty-eight im the space 
of an inch, the stipes bemg usually nearly three fourths of an mch (the 
longest one eighty-three hundredths) in length. 
We have no evidence that the test is punctate, and it has all the ap- 
pearance of the ordmary graptolites. The greatest width observed in any 
stipe, exclusive of the marginal meshes, is seventeen hundredths of an inch. 
In one specimen the extreme length of the stipe, exclusive of the radicles 
and extended axis, is seventy hundredths of an inch; and the width, 
exclusive of the meshes, is fifteen hundredths, and including the meshes, 
twenty hundredths of an inch. 
The specimens examined are all extremely compressed, so that it is im- 
possible to determine any points of structure beyond those presented upon 
the surface. Ido not suppose that the original form has been that of a 
flattened stipe, but rather of a quadrangular or fusiform sac, perhaps even 
convex on one side and flat or concave on the other. The cell-divisions 
are traceable almost to the central axis ; and itis the continuations of these 
that form the reticulation of the margin, and are again produced in seti- 
form spines. It is impossible to reconcile a structure like this with any 
thing previously described among the Giraptolitide ; and though our views 
of their structure may be somewhat modified by an examination of better 
preserved specimens, they cannot be united with the ordmary forms; 
so that while Jetioltes is separated from Graptolithus proper, we may 
regard this form as equally entitled to generic designation. 
EXPLANATIONS OF FigurES OF RETIOGRAPTUS TENTACULATUS, Hall. 
PLaTE XIV. 
6. Anindividual of the natural size, with the marginal reticulations nearly entire. — 
7. The preceding specimen enlarged. 
8. An enlargement of another individual, where the marginal reticulations are 
but partially preserved. 
9. An illustration of a compound form of Retiograpius (R. eucharis), from the 
Utica formation of Lake St. John. (For a description of this species, see 
Appendix.) 
Formation and Locality— Quebec group ; Point Lévis. 
H 
