(;itAi'Ti)r,rn;s of new york, part i 683 



From the former it diflFers by the somewhat closer arrangement of the thecae 

 and their smaller angle of inclination. To the latter it bears such a remark- 

 able similarity of habit that a genetic connection of the two can not be gain- 

 said [p. 5 5 7]. 



Didymograptus acutidens (Lapworth ms. em. Elles & Wood) 



Plate 13, figure 15 



Didymograptus affinis Hopkinson. Quar. Jour. Geol. Soc. 1875. v. 31, 



pi 33, fig.6b,c 

 Didymograptus acutidens (Lapworth ms em. Elles & Wood). Monogr. Brit. 



Grapt.pt 1. Pal. Soc. vol. for 1901. p.25, pl.2, %.3a-d 



DescTtption. Only one specimen of this species has been observed. This 

 presents the following characters. Primary disk and nema not present. 

 Sicula slender, about 1 . 2 mm long, branches originate at 

 slightly different levels, the first theca curving away from 

 a point about two thirds the lens^th of the sicula from ^ig. 77 Didymo- 



'■ " graptus acutidens 



its apex and the second theca nearer to the aperture. tion'^ThfMosome.' "ob- 

 verse view. Deep kill, xo 



Mature length of branches not observed, branches diverg- 

 ing at an angle of 180°; straight, but not rigidly so, very slender, .4 mm 

 wide in the pro .ximal portion and attaining a width of .6 mm. Thecae 

 numbering 11 in 10 mm, four times as long as wide, in contact for one 

 third to one half of their length; inclination 15°. Outer margin straight; 

 apertiiral margin concave with a denticle. 



Position and localities. A single specimen has been found on a slab 

 with Phyllograptus anna, Dichograptus octobrachiatus, 

 etc., belonging to the lower part of the zone with D . b i f i d u s . In Great 

 Britain the same species occurs, according to the monograph of the British 

 graptolite fauna, in the Lower Llanvirn of the St David's district in Wales 

 and of south Shropshire ; hence at about the same level as on this side of the 

 Atlantic. 



Remarhs. This form is in its habit so similar to Bryograptus 

 lapworthi, described above, that, having but one specimen, I would not 



