612 MISS G. L. ELLES ON THE GEAPTOLITE [Aug. 1 898, 



one the stipes diverge at an angle of about 60° ; in the other the 

 base is more rounded, and the initial angle of divergence approaches 

 a right angle. The ultimate angle included between the stipes in 

 both forms is generally from 15° to 20°. 



The stipes are never parallel, but are continuously divergent 

 throughout their length, though I have never seen a specimen from 

 the Skiddaw Slates in which the angle of divergence was as wide 

 as that figured by Hall (ojp. supra cit. pi. iii, fig. 9). The stipes 

 are narrow at their origin, being about -^^ inch (1-26 mm.) wide, 

 but ultimately attain a maximum width of -J^ inch (2*1 mm.). 

 No Skiddaw Slate specimen is known to me in which the width is 

 as great as | inch (6*3 mm.), the maximum dimension given by 

 Hall. The greatest width is attained near the distal end of the 

 stipes, after which there is a somewhat rapid diminution. The 

 increased width is due to the fact that the thecae augment steadily 

 in length from the proximal to the distal portion of the stipes; 

 but at the actual extremities the thecae are only partially developed, 

 and consequently a diminution in width again takes place. One 

 result of this is to give a peculiar curvature to the celluliferous 

 margins ; these have at first a slight concave curvature, but sub- 

 sequently the curve may be convex, or else curvature is con- 

 tinuously concave ; the dorsal walls are at first convex, and then 

 straight. 



The thecae number generally thirty-two to thirty-six in the 

 inch (thirteen to fourteen in 10 mm.) ; they are long narrow 

 tubes, and their length is about 4 times that of their width at the 

 widest part ; they are free for a third to a quarter of their length, 

 and are inclined at an angle of about 45°. The apertures are con- 

 cave and submucronate, and make an angle of about 125° with the 

 general direction of the stipe. 



When fully grown the rhabdosoma measures commonly about 

 1 inch (25-4 mm.) in length ; one specimen from Thornship Beck 

 is, however, 1| inch (31*7 mm.) long, and another from EUergill 

 must have been fully 1| inch (38 mm.) in length. From the 

 appearance of the rhabdosoma in the obverse view, it would seem 

 as if the earliest theca originated from the sicula slightly above 

 its aperture, but in no specimen is the proximal end sufficiently 

 well preserved to make this out with certainty. 



The species is characterized by (1) the form of the stipe with 

 straight dorsal wall and curved celluliferous margin ; (2) the 

 gradual widening of the stipes from the point of origin ; and 

 (3) the characters of the thecae and their number to the inch. 



Occurrence. — With Diplograptus dentatus (Brongn.) at 

 EUergill in the EUergill Beds = Upper Skiddaw Slates. 



Localities. — Barf; Doddick Eell ; Saddleback; Outerside; 

 Burstock Scar, Skiddaw ; Thornship Beck, Shap ; EllergiU ; East 

 Dodd Wood ; Aik Beck, Pooley. 



