394 NEW VORK STATE MUSEUM 



the typical G. quadrimucronatus this variety differs principally in 

 the smaller overlap of the thecae which gives to the profile view the aspect 

 of a Diplograptus foliaceus and the development of the lateral 

 spines. No traces of the differentiation of the test into a continuous and 

 a fibrous layer, observed in G. quadrimucronatus, have been noticed 

 in this species, if not the presence of a solid rim of the 

 aperture, connecting" the two apertural spines is to be 

 taken as indicating" that structure. The nemacaulus is, 

 in the great majority of the specimens, very thin, but in 

 some it has been observed to expand into long fusiform 

 — *^ y "vesicles." 



— t"-^ '"f Glossograptus quadrimucronatus ( Hall ) mut. postremus no v. 



^\^\ - Plate 26, figure 16 



The reduction in the width of the rhabdosomes and 



\Zf the close arrangement of the thecae — both resulting from 



a reduction in the size of the zooids and indicating a 



decadent condition — have gone still a step farther in 



Fig. 343 Glossograp- . , . 



tus quadrimucronatus the Lorraine mutation, which has been observed in the 



var. postremus nov. 



n. y. °x°s me ' lower beds at Waterford, above Mechanicville, Frankfort, 



and in other places. The width is here reduced to 2 mm and the number 

 of thecae has risen to 12 to 16 in 10 mm (30-40 in the inch). 



Glossograptus whitfieldi (Hall) 



Plate 26, figure 17 



Graptolithus whitfieldi Hall. Pal. N. Y. 1859. 3 15 16, fig. 1 

 Graptolithus whitfieldi Hall. N. Y. State Cab. Xat. Hist. 13th Rep't. 



i860, p. 60, fig. 1 

 Graptolithus whitfieldi (in part) Hall. Can. Org. Rem. Dec. 2. 1865. 



p. 31, fig. 29; p. 36, fig. 31; non pi. B, fig. 6— 11 

 Diplograpsus whitfieldi Nicholson. Geol. Mag. 1867. 4: in ; pi. 7, fig. 4, 



4a 

 Graptolithus whitfieldi Hall. N. Y. State Cab. Xat. Hist. 20th Rep't. 



1868. p. 199, fig. 31 





