646 NEW YOUK STATE MUSEUM 



Tetragraptns quadribrac hiatus Ruedemann. N. Y. State Paleontol. An 



Rep't. 1902. p.556 

 Tetragraptns qnadribrachiatns Elles & Wood. Monogr. Brit. Grapt. ptl. 



1902. p.57, pl.5, fig.la-d 



Description. Pnraary disk and nema not observed. Sicula present, 

 but observed only in sections. Branch of first order 2 . 6 mm long, consist- 

 ing apparently of two thecae on either side. Four branches of the second 

 order, which are spread out horizontally ; straight, slender, rigid, increasing 



very gradually from a Avidth of . 6 mm to one 



^^ A of 2.4 mm, attaining a maximal length of 



^T^^^ ^^ 42 mm. Thecae 8 to 9 in 10 mm, inclined at a 



^^^^^^ low angle (about 35-40°), narrow (four times 



^F ^k as long as wide), overlapping for one half to 



▼ ^mk one third of their length. Outer wall slightly 



curved. Apertural margins straight or slightly 

 ^ „ .„  concave, normal on the axis of the thecae. 



Fig. 51 Tetrasrrapt us quadri- 



8ome':''i^p"^i..^£'5'''- "^"""^ '"^"^"^ Position and localities. In the Deep kill 



section this species has been found in great 

 number in graptolite bed 2 (Tetragraptus zone), less common in 

 bed 5 and in but a single specimen in graptolite bed 7 (zone with Diplo- 

 graptus dentatus)^. It is also common in a band of sandy slate, out- 

 cropping between Defreestville and West Sandlake, Rensselaer co. N. Y. 

 [T. N. Dale, coll.] ; and one small specimen has been observed in the shales 

 with Diplograptus dentatus at Mt Moreno near Hudson N. Y. 



Hall's specimens came from the lower shales of Point Levis (Tetra 

 graptus horizon or Main Point Levis zone of Gurley). Matthew collected it 

 also in the St John basin. In Great Britain the species occurs in the mid- 

 dle and upper beds of the Middle Skiddaw slates in the Lake district at 

 numerous localities ; in the St David's district in Wales and in the Ballantrae 



'The latter may belong to a somewhat different later mutation, as the greater 

 proximal width of its branches would suggest, but it is not in a sulBciently good state of 

 preservation to decide this point. 



