GRAPTOLITES OF NEW YORK, PART 2 475 



Along the apertural and ventral margins run distinct fibrous thicken- 

 ing's of the periderm [see text fig. 457, 465 | which in form and position cor- 

 respond to the mouth ledges of Glossograptus. In macerated specimens 

 [see pi. 30, fig. 2] horizontal ledges are seen to proceed from nodes of the 

 nemacaulus [see text fig. 463] and to form by reaching beyond the thecae the 

 long, diverging fibers between which the "reproductive sacs" are enclosed. 



The only comparable structure with which we are acquainted are the 

 strengthening bands of Climacograptus retioloides Wiman [see 

 text fig. 50, p. 124]. These thickenings of the middle layer of the periderm 

 are described by Wiman [1895, p. 38] as passing horizontally outward along 

 the double longitudinal septum, then turning at right angles and crossing 

 the proximal parts of the thecae until the)' reach the interthecal walls, when 

 they bend upward under 45 and unite at the bases of the loops on the 

 ventral walls of the thecae. The great similarity in form of these loops to 

 those of the apertural fibers of Lasiograptus is in this connection of especial 

 sionificance as indicating another structure common to C. retioloides 

 and to Lasiograptus. Wiman's view that this form throws some light upon 

 the Retiolitidae and Freeh's that it, on account of its loops, may have led 

 to Lasiograptus, are both supported by the presence of like strengthening 

 bands in the rhabdosomes of Lasiograptus. Moreover, a comparison of 

 Wiman's figure with those of Lasiograptus [as pi. 30, fig. 5] will at once 

 bring out the singular similarity in the shape of the thecae of this Climaco- 

 graptus and of Lasiograptus. From our observations, here recorded, we 

 infer that the periderm of Lasiograptus was extremely thin and supported 

 by strengthening bands, one of which had the direction above described and 

 another of which surrounded the aperture. 1 



Probably there had also begun the formation of a fine fibrous network 

 in the periderm, corresponding to that of other Retiolitidae, for traces of 

 such have been noticed in several specimens. 



We will now turn to the appendages. In the great majority of the 



1 It is also noted by Wiman that in C. retioloides the margins of the apertures 

 are thickened. 



