650 NEW YORK STATE MUSEUM 



Tetragraptus fruticosus Roemer & Freeh. Lethaea palaeDzoica. 1897- Bdl, 



p.602 

 Tetragraptiis fruticosus Rnedemaun. N. Y. State Paleontol. An. Rep't. 



1902. p,554r, 556, 566 ; p.588, fig.l5 

 Tetragraptus fruticosus EUes & Wood. Monogr. Brit. Grapt. ptl. Pal. 



Soc. vol. for 1902. 1902. p.61, pl.6, fig.2a, b 



Description. Sicula long (about ,3.6 mm), and slender. Provided in 

 yonng colonies with, a short, thin nema which in one case [pl.9, fig.l4] has 

 been observed to terminate in a small concentrically wrinkled, chitinous disk 

 (diameter = 1 . 3 mm). Mature rhabdosome suspended by means of a long, 

 stout nema, or nemacaulus, which attains a width of 1.5 mm (in compressed 

 state) and gradually tapers to a fine thread. Total length of nema unknown, 

 but in a mature specimen a fragment of 30 mm in length has been observed, 

 which did not show any decrease in its width. First, theca budding in the 

 apical third of the sicula ; first and second thecae adhering to the sicula till 

 near its aperture ; each of these thecae producing two branches by dichotomy. 

 Two pairs of gracefully and symmetrically curved branches, which give to 

 the rhabdosome a bell or lyre-shaped outline ; the branches attain a length of 

 10 cm and more, and a width of 3.5 mm, and diverge at an angle of about 

 40°. The reftection of the branches takes place at various distances (18 to 

 48 mm) from the aperture of the sicula. The branches increase gradually in 

 width up to the point of reflection, when they become approximately uniform 

 in width. Thecae short and broad in the proximal parts of the branches, 

 long, narrow and mucronate in the mature parts, six being counted in the 

 space of 10 mm in the former and eight within the same space in the latter. 

 The early thecae overlap about one half their length, the mature ones are in 

 contact nearly their entire length ; the former form an angle of about 20° 

 with the axis of the stipe, the latter one of 40° ; the apertural margins of the 

 nepionic thecae are straight, their upper margin is not protracted into a 

 mucro, while the apertural margins of the mature thecae are deeply concave 

 and their upper margins mucronate. 



