646 NEW YORK STATE MUSEUM 



Tet rag rapt US quad ribrac hiatus Ruedemann. N. Y. State Paleontol. An 



Rep't. 1902. p.556 

 Tetragraptus quadribrachiatu s Elles & Wood. Monogr. Brit. Grapt. ptl. 



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



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

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

 ing aj^parently 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 ^vidth of . 6 mm to one 

 of 2.4 mm, attaining a maximal length of 

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

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

 as long as wide), overlapping for one half to 

 one third of their length. Outer wall slightl}^ 

 curved. Apertural margins straight or slightly 

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



Fig. 51 Tetragraptus qua dri- 



some':*'itepliii.''x4./'^- ^°"°=^ '''^''^°- PosUion 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 D i p 1 o - 

 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 Grurley). Matthew collected it 

 also in the St John basin. In Great Bi-itain 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 saggest, but it is not in a suflicieutly good state of 

 preservation to decide this point. 



