GRAPTOLITBS OB' NEW YORK, PART 1 001 



The different direction of compression alters the aspect of this species 

 very considerably. The distinctive characters cited before suffice ho\vever 

 fully for its recognition in all cases. We have figured some of the more strik- 

 ing aspects. It appears that, on the Avhole, the branches of the Deep kill 

 specimens are somewhat narrower, or at least do not reach the maximal width 

 cited by Hall and Elles, while in all other respects, specially the length which 

 they attain, they do not differ from the descriptions given by these authors. 



In a paper on the growth and development of G o n i o g r a p t u s 

 t h u r e a u i , the writer figured two extremely minute, apparently young 

 specimens of a Tetragraptus, which he then thought 

 referable to this species. Subsequent investigation has 

 shown, that notwithstanding the resemblance between 

 these and the mature specimens of T . s i m i 1 i s , the 

 young of the lattei- form are quite different, their sic- 

 ulae being larger and stouter, and not proiectine below k^. 6i TetraKraptus 



° ° >- ^- similis Hall su. Frag- 



the first few thecae. As these minute rhabdosomes could ^^"'"show'' thrchara'Senft'ic 



,  /• ni 1 aspect of the thecae In the 



not be referred to any other species oi 1 eti'agraptus, they compr^d condition. Deep 

 have been described as a new type ( T . p y g m a e u s ) . 



Holm succeeded in isolating specimens of T. similis (bigsbyi) 

 and thus elucidating the structure of the proximal parts. He also gives 

 figures of a very young specimen, showing the " Didymograptus stage," i. e. 

 the sicula, the left and right thecae and the coimecting canal. Some of his 

 instructive figures have been copied in the discussion of the genus. 



The siirfaces of graptolite bed 2 at the Deep kill are covered with 

 growth stages of this species. These verify Holm's observations, so far as 

 their flattened condition permits the study of their original structure. We 

 figure several of these stages which exhibit important features [pl.l2, fig.8-10]. 

 Specially remarkable among them is the veiy long, extremely thin filamentary 

 nema, which in one specimen [fig.lO] is seen to end in a relatively large, 

 thinly chitinous disk with a somewhat thickened central part. 



Very frequently the two branches of one side alone are preserved 

 [fig,58], whereby the fossil receives the appearance of a Didymograptus, of 



