GRAPTOLITES OF NEW YORK, PART 2 



83 



Various forms are here possible according to the relative development of 

 the two groups of wings. In text figure 15 the wings on the spines are 

 but little developed, but the later disk-forming wings the more; in 

 others as in text figure 13 the earlier outgrowths of the spines are so 

 strong that in the compressed stage they cover the later disk more or less. 

 A fourth group (tridentatus Lapworth) originates from the 

 stronger development of the virgella or sicular spine besides the two lateral 



Fig. 12-17 Climacograptus bi cornis Hall. Sicular ends showing the lateral spines and "wings." x 5 



spines. It will be noticed that many of the bicornis forms, as 3, 6, 8, 

 9, 11, show already a short, blunt virgella. But in some forms it takes 

 a spurt and grows out way beyond the lateral spurs, as in 36 and t>7- 

 In a few specimens as in 32 it even develops its own wing, while in others 

 [_33] ^ remains fine and hairlike like the lateral spines. This triden- 

 tatus variety rarely may become combined with the pelt if er form as 

 in 34 and no doubt also with the" sign urn form. The lateral spurs 



