662 NEW YORK STATE MUSEUIM 



the group of D. caduceus. The two forms have no doubt been fre- 

 quently confused for this reason. The character of the thecae and the differ- 

 ent width of the proximal parts of the rhabdosomes furnish however a read^^ 

 means of distinction. Young colonies also frequently become so obliquely 

 compressed that both pairs of branches fall into one plane, each pair forming 

 a horseshoelike curve, and the primary thecae and sicula together become 

 visible [pl.l2, fig.4]. Older specimens are nearly always laterally compressed. 



Tetragraptus woodi sp. nov. 



Plate 13, figures 1, 15, 16 



Tetragraptus bigsbyi Kuedemann {pars). N. T . State Paleontol. An. Rep't. 

 1902. p.556 



Description. Primary disk unknown ; nema very thin, filiform. Rhabdo- 

 some of small size (about 19 mm in length). Sicula conspicuous, about 

 1 . 7 mm long ; first theca originating near the apex of the sicula, apparently 

 of like character and direction of growth as in T. similis; first and second 

 thecae forming two branches of the first, order, which have a horizontal direc- 

 tion. Branches of the second order 17 to 19 mm long in their mature state, 

 approximately straight or curving outward, directed obliquely upward, 

 diverging under angles of 30° to 50° ; mostly under 40° in the compressed 

 state ; widest at the base (2 . 2 mm), and diminishing regularly toward the 

 distal end to 1.4 mm. Thecae about 16 in 10 mm in the proximal portion, 

 and quite constantly 12 in the same space in the distal portion ; curved, 

 strongly inclined (about 50°) ; widening toward the aperture, twice as wide 

 at aperture as at base ; short (1 .4 mm near base) ; twice as long as wide (in 

 distal parts of branches) ; in contact one half to three fifths of their length ; 

 ajDertural margin approximately straight if fully exposed, but as a rule 

 appearing curved and slightly oblique to the axis of the thecae in distal 

 thecae, producing with the concave outer maa-gin a recurved apertural 

 denticle. 



Position and locality. Found as the predominant form in a single sur- 

 face of graptolite bed 2 at the Deep kill, associated with Groniograptus 



