GRAPTOLITES OF NEW YORK, PART 2 



2 57 



was the two branched Didymograptus. In Europe one 

 has known for a long time a last and final stage in which 

 still one of these two last branches has been lost and the 

 one branched staoe been reached that is known under the 

 generic term Azygograptus. 



Professor Lapworth has recognized a form of this 

 type in the Normanskill shale material from Stockport, 

 N. Y. sent to him by Dr Gurley for investigation and has 

 described it as A. ? w a 1 c o 1 1 i. We have referred here 

 another form, A. ? simplex, with some doubt to this 

 curious genus, our doubt being mainly due to the fact that 

 we have no conclusive evidence that this fossil is not a 

 growth stage of a larger, unknown graptolite. As we 

 know it, it consists, in its most complete form, of the sicula 

 and one theca only. If this be the mature organism, then 

 it certainly represents the last possible stage of reduction — 

 save the mere sicula — in the Dichograptidae, the last 

 remaining branch of the once richly branching rhabdo- 

 some being reduced to but one theca. 



Azygograptus ? walcotti Lapworth 



Gurley has published [1896, p. 69] the following 



description of this form from Lapworth's manuscript : 



Polypary unilateral, monoprionidian, consisting of a 

 single flexuous and simple compressed branch proceeding 

 almost horizontally from the side of an inconspicuous sicula, 

 50 to 75 mm in length, in average diameter about 0.5 mm. 

 Thecae 16 in 25 mm, without overlap, consisting of conical 

 tubes, increasing slightly in diameter throughout, adnate 

 to the coenosarcal canal, with straight or slightly convex 

 ventral margins. Apertural margin a little inclined and 

 projecting from the ventral margin for a distance equal to 

 about one half the diameter of the polypary and trans- 

 gressing upon the periderm for a similar distance. Denticle 

 almost rectangular ; excavations and interspaces shallow 

 and inconspicuous. 



and added the following comment : 



Fig. 

 1 11 s 



162 A z y g c 

 > walcotti 



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