376 NEW YORK STATE MUSEUM 



former corresponding to Graptolithus s p i n o s u s Hall, the latter to 

 G 1 oss ograp tus ciliatus Emmons. A large series of specimens, like 

 that from Glenmont, will however always furnish a few which, as that 

 represented in plate 27, figure 1, are so broken or twisted as to exhibit both 

 aspects. In plate 27, figure 2 both sets of spines are seen overlapping on 

 one side of the rhabdosome. 



The writer has already, in an introductory chapter on the morphology 

 of spines discussed the probable causal connection of the spines and the 

 origin of the framework of the periderm. There is no doubt that in Glosso- 

 graptus a strong retioloid framework existed though it is covered by a thick 

 outer or epidermal layer and therefore only exposed in macerated specimens. 

 This structure had been recognized by Gurley, as appears from a note on 

 Glossograptus found in his manuscript. 



note. (July, 1895.) I have made a number of attempts to decipher 

 the structure in Glossograpsus, but so far the specimens seen have not been 

 good enough to figure. This much, however, may be safely asserted : The 

 structure in general accords with that in the other retiolitoid genera ; parietal 

 ledges are certainly present and mouth ledges also. Y\ nether the cross- 

 section was quadrangular or hexagonal is not very much important, it being 

 merely a question whether the two halves of the lateral surface meet at a 

 decided an<de ; the whole lateral surface is rounded convex. A much more 

 important point is the number and character of the virgulae. On this point 

 the material affords no clue. I have never seen any indication of a second 

 virgula, though from analogy it is inquirenda. 



We reproduce here in plate 27, figure 3 and text figure 329, specimens 

 in which the outwardly curving horizontal mouth ledges and the convex 

 lateral ledges are distinctly shown and in plate 27, figure 5 part of a specimen 

 in which the epidermis is entirely lost and a meshwork exhibited, which, to 

 all appearances, is like that of the Retiolitidae. Besides this structure, the 

 figured specimen possesses three well preserved threadlike axes, the; middle 

 one of which is stronger and straitrhter than the rest which arc slisjhtly 

 undulating. In the great majority of specimens the middle axis alone is 

 visible. This is evidently i\uc to the fact that the rhabdosomes as a rule 

 are resting on one of the frontal or lateral faces and that only in obliquely 



