GKAPTOLITES OF NEW YORK. PART 1 bb6 



perflexilis, Tetragraptus friiticosus, Didymograptus 

 n i t i d u s . 



Remarhs. This form agrees in the character of its thecae fully ^nth 

 T. (bigsbyi) similis and has therefore been first considered by the 

 writer as a variety of that species. The constancy and importance of its 

 differential characters, and the absence of transitional f onus to T . similis 

 are, however, sufficient evidence of the fixation of this type and of its 

 specific value. It differs from T . similis principally by the greater 

 length, straight direction, obliquely outward gro\vth and regular tapering of 

 the branches. In its central portion and the basal parts of the secondary 

 branches it does not differ materially from T . s i m i 1 i s . I't, therefore, repre 

 sents undoubtedly a further development of that species in a direction, how- 

 ever, different from that leading to Phyllograptus. 



Tetragraptus taraxacum Ruedemann 



Plate 12, fig-ures 17-26 



Tetragraptus taraxacum nom. nud. Ruedemann. N. Y. State Paleontol. An. 

 Rep't. 1902. p.589, fig.l6 



A small but very characteristic form, which is easily recognized among 

 the multitude of species intermixed on the slabs of the Tetragra^Jtus beds 

 (graptolite bed no. 2). 



Description. The sicula is middle sized and slender (1.8 to 1.7 mm). 

 The two primary thecae, the first of which buds in about the middle of the 

 sicula, are veiy long, cylindric (1 to 1.4 mm) and diverge at approximately 

 right angles fi'om the sicula. The four ultimate bi'anches which spi'ing from 

 the same are gently curved upward to such an extent that they rise only a 

 little above the apical end of the sicula. The angle of divergence between 

 each pair of branches apparently amounted to as much as 180". Their aver- 

 age length is 6 mm; greatest Avidth 1.4 mm; greatest length observed 9.7 mm. 



The first theca of each branch is still long and tubular and provided with 

 a straight apertural margin as the primary thecae ; the following thecae 

 assume rapidly a very different aspect by widening strongl}' to^vard the 



