486 NEW YORK STATE MUSEUM 



The distal end of the theca is the aperture. In describing the thecae, 

 one regards them as bounded by four walls, viz one dorsal (inner), one ventral 

 (outer), and two lateral walls. The distal free margins of these walls consti- 

 tute collectively the apertural margin. The ventral region of the apertural 

 margin forms a well marked denticle and is sometimes prolonged into an 

 apertural spine. The length of the thecae is conventionally measured by the 

 ventral margin. The latter is in contact with the dorsal wall of the theca 

 immediately preceding it, or overlapped by it to a certain fraction of the length 

 of the thecae. 



The walls of the rhabdosomes, which in the living state were chitinous, 

 are cited as the periderm, perisarc, test, Haut and Schale. 



The proximal parts of the thecae form a canal in the Graptoloidea. This 

 is termed the common canal, coenosaroal canal, gemeinsamer Canal, canal 

 commun. The outer edge of this common canal is termed the dorsal edge. A 

 view of the compressed stipes, in which only this canal is exhibited, is a dorsal 

 view. The opposite margin, which is denticulated by the outer margins of the 

 thecae, is the ventral margin, and the corresponding view is the ventral or 

 frontal view (scalariform aspect). In the profile view both the dorsal and 

 ventral edges are seen. 



Hall proposed the term funicle for the central connecting process and its 

 subdivisions in the Dichograptidae, which he thought to be destitute of thecae. 

 Since, however, these central parts have later on turned out to be also com- 

 posed of thecae, the term is no longer applicable to them. The writer [1895, 

 p.222] had applied Hall's term to the small, long elliptic chitinous vesicle from 

 which the nemacauluses of Diplograptus spring. Wiman [1895, p.73] has 

 pointed out that this so called funicle of Diplograptus is a different part of the 

 graptolite colony from that which Hall termed funicle in the Dichograptidae ; 

 he concedes however that it may be identical with the part of Retiograptus 

 called funicle by Hall. As, indeed, the composition of the synrhabdosomes of 

 Retiograptus and Diplograptus is identical, both representing persons of the 

 third order, and the central parts, termed here funicle, are stems which are 

 destitute of thecae, the term no longer necessary for the Dichograptidae could 



