Some Recent Graptolitic Literature. — Gurley. 43 
square-prismoid polypary. From each convex angle of the zig-zag and 
from a corresponding level of the straight virgula, there extends out- 
ward in the reticulated wall of the polypary, a chitinous bar ( "parietal 
ledge"). In the ventral ( outer ) wall of the polypary the parietal ledges 
are connected by a horizontal "mouth-ledge." Tracing the parietal 
ledges back toward the central line of the polypary they are seen to be 
deflected upward in the vertical and inward in the horizontal plane so 
that they sink below the surface, i. e., into the interior of the polypary. 
Near the point of deflection they are connected by a bar which traverses 
the interior of the polypary ( "inner cross ledge"). On the trapezoidal 
frame formed by the mouth-ledge, inner cross ledge and two parietal 
ledges is strung a fine chitinous network which is an inward extension 
of the exterior network serving to divide adjacent thecte. The external 
network Is stretched over the whole surface of the polpary being attached 
on the ventral surfaces, to the mouth-ledges and on the lateral surfaces 
to the parietal ledges as far as the point where those ledges become de- 
flected below the surface. At this point the attachment to the ledges 
ceases and the network is stretched across the median line to the sim- 
ilar angle of the opposite parietal ledge. From all this it follows that 
three canals extend the length of the polypary in the median line. The 
central of these is the common canal which is bounded on either side 
by the inner cross ledges and front and back by the two virgulas. Be- 
tween this canal and the network (stretched across from angle to angle 
as described above ) lie two canals, one in front of and one behind the 
common canal. It is thus easy to see what diverse appearances may be 
presented by one and the same polypary under different degrees and 
directions of pressure. Preserved In relief neither virgula is visible ; 
the external network with the parietal ledges extending toward but 
stopping short of the center being all that can be seen, while if subjected 
to compression, the zig-zag, or the straight virgula (or with greater 
pressure, both the zig-zag and the straight virgula) becomes visible. 
The specimen which has furnished this description fails to show an 
outer envelope or inner dividing walls, but the author cites several 
authorities to prove the existence of these structures. 
In a general way the structure of Stomatograptus tor?i(inisti resembles 
that of R. geinitzkinus. The epidermic coating of the network is, how- 
ever, coarser and the virgulas and ledges finer than in the latter species, 
and the plane of the thecal mouths is oblique to the long axis of the 
polypary so that in profile the latter appears serrate. In a well preserved 
specimen of S. tornquisU Mr. Holm detected an epidermic layer external, 
and an endermic layer internal to the network. The outer and inner are 
smooth and without gaps, the middle alone being cribriform. 
Our author believes (but was not able to demonstrate) that interiDi-ly 
the inter-thecal partition planes are attached to the inner cross ledges. 
He further believes (in opposition to Tullberg's opinion), that the 
thecae were not delimited interiorly by a porous membrane from the 
common canal but that the communication between the two was un- 
restricted. 
The remainder of this admirable article is devoted to a criticism of 
Jakel's essay which has been noticed above. 
