GRAri()Lrri:s of .mow york, part i 699 



Didymograptus forcipiformis sjj. uov. 



Plate 15, flsrures 10 1» 



Description. Primary disk not observed. Nema filamentous, extremely 

 thin. Sicula long and slender (length about 3 . f> ram). Two branches, bent at 

 their bases to such a degree that their distal parts, which are straight, become 

 subparallel (angle of divergence 350° or more) ; they attain a considerable 

 length (24mm), are wide at their bases (3 mm), but taper rapidly to a width 

 of . 6 mm oi- less. Thecae long in the basal part of the branches (3 mm), but 

 becoming shorter in the distal portions, where they are more inclined (45°) ; 

 numbering but .9 to 10 in 10 mm, curved, about three 

 times as long as wide, in contact throughout their length. 

 Apertural margin slightly concave, lower part produced 

 into a mucro or short spine in the distal ])oj'tion and 

 into long spines in the long, proximal thecae. 



Position and locality. This species has been observed 

 only in the beds with Diplograptus dentatus 

 at Mt Moreno near Hudson, in one layer of which it Fig.9i Didymograptua 



forcipiformis 9p. nov. 



occurs quite frequently. g^^ portic,„^ of^ bj^^nch. 



Memarhs. D. forcipiformis differs from 1). 

 caduceus Salter, of which it is a late derivative, by the greater divergence 

 of the branches, by the smaller width of the distal portion of the branches 

 and their greater rate of tapering, the great width of the proximal portion of 

 the branches, the less close arrangement of the thecae and the presence of 

 mucros or spines at the apertural margins. 



EUes and Wood state that there occur among the British forms of D . 

 gibberulus Nicholson (=D. caduceus nobis) several mutations, in one 

 of which " the dorsal walls of the stipes are straight distally, the stipes run- 

 ning parallel to each other". Our form agrees with this mutation in the 

 general direction of the branches, though the branches in D. forcipiformis 

 approach each other still much more than they do in the examples figured by 

 Elles. In fact, none of the European forms which I have seen figured appear 



