384 NEW YORK STATE MUSEUM 



G. ciliatus \_comp. pi. 26, fig. 4 and fig. 8]; consequently they will 

 often both appear in the same view of a specimen and produce a thick 

 crown of spines. While in G. ciliatus the spines of the lateral faces 

 are rather stout, spurlike, straight and diverted obliquely upward, they are 

 here thin, hairlike and horizontal in direction [see pi. 26, fig. 9]. The width 

 and length of the rhabdosome seem to be the same as in the Normanskill 

 types, but the sicular extremity is less rounded and the whole rhabdosome 

 more gradually widening, hence the lateral margins never so strictly 

 parallel as in G . ciliatus. The sicula and the characters of the thecae 

 have not been observed. 



Position and locality. This mutation is found in dark brown shales at 

 Summit, Nev., where it is associated with Phyllogr. anna, Cli- 

 macogr. caelatus, Cryptogr. tricornis and Caryocaris. 



Glossograptus ciliatus Emmons var. debilis nov. 



Plate 26, figures 6, 7 



Description. Synrhabdosome not observed. Rhabdosome small (16 + 

 mm long), narrow (width of side i mm), with parallel margins. Nemacaulus 

 thin, protruding to length of rhabdosome. Sicular and antisicular extremi- 

 ties rounded. Spines as in G. ciliatus. Sicula not observed. Thecae 

 very closely arranged (16-22 in 10 mm), shorter than in G . ciliatus, 

 but apparently not differing in overlap and inclination. 



Position and locality. In the Normanskill shale of Mt Moreno near 

 Hudson. 



Remarks. This variety covers in great number a layer at Mt Moreno. 

 Its differences from the typical ciliatus, which consist in the smaller size 

 and width and greatly closer arrangement of thecae, are uniform. These and 

 the frequent irregular bendings of the rhabdosomes give the form the 

 appearance of a weaker variety of G. ciliatus which lived under less 

 favorable physical conditions. Held side by side with the sturdy specimens 

 of G. ciliatus from Alabama, the contrast is still more striking. 



