490 Dr. Gerhard Holm — On the Structure of Oraptolites. 



Tetragkaptus Bigsbyi, Hall. 



Figs. 9-12. — Proximal part of a specimen obliquely broken across the sicula and 

 right theca — see Fig. 9 — by the fracture of the rock. The pieces were 

 cemented with Canada balsam, and both parts of the Tetragraptus 

 specimen subsequently isolated. — Enlarged 6 diameters. 



Fig. 9. — The more complete part, from the sicula side, showing the proximal part 

 of the sicula, the left theca, the anterior left branch, and the passage 

 between the connecting canal and the right theca. 



Fig. 10. — From the left side, showing the left theca seen from the aperture, the 

 proximal part of the sicula, and the anterior and posterior left branches. 



Fig. 11. — From the anti-sicula side, showing the connecting canal and the sicula 

 behind, the left and right thecse, also the posterior left branch and the 

 posterior right branch ; in the latter the first theca is complete and the 

 remaining ones show only the apertures. 



Fig. 12. — From the proximal end, with the sicula side turned downwards, showing 

 the apertures of the sicula, left and right thecse, and the thecse of the 

 four branches. 



Fig. 13. — Proximal part of another specimen lying in the rock, partly in relief, 

 partly in impression. From the anti-sicula side. The connecting canal 

 and the wall between that and the sicula have, however, remained in the 

 counterpart, so that the smooth cast of the sicula appears uncovered. 

 The left theca in impression, the right theca complete with fractured 

 surface at the junction of the connecting canal. — Enlarged 6 diameters. 



Fig. H.^Another specimen. Proximal end, also lying in the rock, seen from anti- 

 sicula side, showing the connecting canal. All the branches are broken 

 off near their point of origin. — Enlarged 6 diameters. 



Fig. 15. — Young specimen with posterior left branch complete. Anterior right 

 branch injured near the apex, and both the remaining branches broken 

 off near their point of origin. Anti-sicula side seen a little from the left, 

 so that the aperture of the right theca appears, showing sicula, right 

 theca, and connecting canal ; the apertural part in the left theca is 

 broken off. Isolated by means of acid. — Enlarged 6 diameters. 



Fig. 16. — Isolated. Much injured specimen, showing sicula, left and right thecse, 

 and both anterior branches. Posterior right branch is missing, and 

 only the first theca of the posterior left branch remains. — Enlarged 

 6 diameters. 



EXPLANATION OF PLATE XIV. 



PhYLLOGKAFTUS ANGUSTirOLIUS, Hall. 



Fig. 1. — Sicula side, seen a little from the right, showing the cornet-shaped sicula, 

 visible for the whole of its length, with the apertural margin turned 

 somewhat to the right ; to the left of this the left theca, also with its 

 cornet-shaped proximal part lying along the left side of the sicula, but 

 turning the apertural portion and aperture obliquely downwards to the 

 left. To the right of the sicula, the right theca directed obliquely 

 downwards, with the aperture turned to the right. Above this the 

 thecse lying in the plane of the paper and directed obliquely forwards ; 

 to the left the anterior left, and to the right the anterior right, series 

 of thecse. Behind the latter appears the outline of the posterior right 

 series of thecse. 



Fig. 2. — Eight side, seen a little from the left, showing the lowest of the right 

 thecse with the aperture turned forwards towards the spectator, and above 

 it, to the left, the anterior, to the right the posteiior, right series of 

 thecaj. On the left side, behind the former, the apices of the anterior 

 left series of thecse appear, and behind the right theca the apex of the 

 aperture of the sicula. 



Fig. 3. — Anti-sicula side, seen somewhat from the right, showing the aperture of 

 the sicula directed obliquely forwards to the left ; to the left of this the 

 right theca in profile, and to the right the left theca. Above this, to 

 the left, the posterior light, and to the right the posterior left, series of 

 thecse. On the right side we get a glimpse behind of the outlines of the 

 anterior left thecal series. 



