Br. Gerhard Holm — On the Stniciure of Graptolites. 487 



and the common canal belonging to the right theca and right branch. 

 The edge of the aperture in the right theca Ls injured, but the inter- 

 thecal wall, which separates this from the anterior and posterior oldest 

 thecaj of the right branch, is conspicuous. The anterior right branch 

 Ls completely cleared away, and only a narrow border of the base of 

 the posterior branch remains. The large opening shows the connection 

 (common canal; between the two right branches. The projecting edge 

 of the same is formed by a diaphragm-like intercalated lamella. — 

 Enlarged 20 diameters. 



Fig. 2. — The proximal part from the anti-sicula side, with the external walls of the 

 connecting canal and the right theca removed in order to .show the 

 interior of the connecting canal and its relation to the common canal. 

 The sicula, the apeitural margin of which is perfect, appears in relief 

 within the connecting canal ; the same is the case with the left theca, 

 the foramen of which touches the sicula wall. On the right side, the 

 common canal for the left branch arises ; on the left, that belonging to 

 the right theca and right branch. Of the distal interthecal wall of the 

 right theca the further part remains. The posterior right branch is 

 completely removed, and only the base of the anterior remains, showing 

 the curved inner edge of the interthecal wall between the first and second 

 thecse of the latter branch.— Enlarged 30 diameters. 



Fig. 3.— Same specimen as Fig. 9, PI. XIII. Longitudinal, vertical section of the 

 sicula, on the sicula'side of the polj-pary, showing the interior of a part of 

 the left half of the sicula, and to 'the "right of this a transverse section 

 of the connecting canal. The foramen between the sicula and left theca 

 IS not visible, as it lies higher up within the part of the proximal end of 

 the sicula, which has not been cut away. — Enlarged 30 diameters. 



I = Sicula. II = Left theca. Ill = Eight theca. 



Genus Phtllograptcs, Hall- 

 No description of the structure of the proximal end, founded on 

 actual or certain observations, is known. Hall thus summarizes, in 

 his generic description, what he knows of the proximal end : " The 

 whole supported on a slender radicle or combined in groups" ; and he 

 believed that, since the proximal end was provided with a "radicle," 

 the majority were free in the same manner as in Liplograptm, whilst 

 others were attached in groups to some support which bore them. 

 In the figures only P. typv.s, Hall, is shown with a long cuneiform 

 diminishing "radicle," which according to the description sometimes 

 approaches^half an inch in length. In the remaining three species 

 the radicle is not visible, and it is described in the text as "minute" 

 or " scarcely visible." 



Lapworth, although he probably did not possess a good specimen 

 of Fhyllograptus, and therefore could not observe the development 

 of the polypary, as early as 1873 rightly interpreted the same and 

 the position of the sicula: " Polypary composite, being essentially 

 a quadribrachiate monoprionidian polypary, whose branches coalesce 

 by the whole of their dorsal surfaces; sicula embedded— the major 

 extremity forming the proximal end of the adult polypary." The only 

 observation on the sicula in Fhyllograptus agreeing with the reality 

 is that given by Tornquist (Siljan. Grapt., i, p. 20), where in 

 P. densus, Tornq., he "believes himself to have observed a sicula 

 with a jutting-up apex, between the most proximal thecal circle"; 

 he adds, however, that this requires confirmation. 



According to Tornquist, the thecse should be situated in four 



