GRAPTOLITES OF NEW YORK, PART 2 465 



peridermal layer, at least in the sicular moiety of the rhabdosome \see 

 below]. In the middle of this face the zigzag axis can be seen pressed into 

 the periderm, and on either side a row of pentagonal meshes, while on the 

 right hand side a row of apertures, consisting of square meshes is shown. 

 The three rows of meshes seen in compressed specimens correspond, hence, 

 to the two rows of one lateral face and one apertural row of meshes. Plate 

 31, figure g is the counterpart of the same specimen. This shows the two 

 rows of skeletal meshes themselves at the right side and at the left side, in 

 consequence of the breaking away of a part of the rhabdosome, one of the 

 lateral rows of the meshes of the opposite side. In the original of plate 31, 

 figure 14 the same three rows of meshes are preserved and also the under- 

 lying three rows of the opposite side, so that altogether there were six rows 

 in the walls of the rhabdosome. 



Gurley's first figure (445) is according to this explanation a frontal 

 view, with the apertural meshes in the middle, while the last figures (447 

 and 448) represent lateral views with the apertural meshes showing along 

 the margins. His second figure is a view corresponding to our figures 9 

 and 11, as indicated by the apertural spines along the margins. Plate 31, 

 figure 12 illustrates a not infrequent case, when four rows of meshes appear. 

 This is due to an oblique splitting of the rhabdosome, thus that the two 

 lateral rows of the upper and under side come to lie side by side. 



Our remaining figures serve to show the sicula [pi. 31, fig. 15] and the 

 additional apertural structures [pi. 31, fig. 10]. The sicula is minute (1 mm 

 long), but apparently covered with a continuous periderm, protruding 

 beyond the rhabdosome and furnished with a short virgella [fig. 10]. Plate 

 31, figure 13 is a reproduction of a beautifully preserved specimen which 

 shows (at sicular end) that the mouth ledges did not lie at the extreme 

 distal end of the thecae, but that the outer or ventral wall of the thecae 

 continued obliquely upward and outward beyond the plane of the meshes 

 for a distance of about one fourth the length of the meshes thereby also 

 giving us an indication of the inclination of the thecae. This outer, roof- 

 like part of the thecae is held at both sides by the mucros proceeding from 



