Lapworth — Graptolites of Co. Down. 
139 
only. Suture deep, zigzag, having each angle prolonged in a short 
horizontal groove. Virgula distally prolonged. Hydrothecae 28 to 
36 in the space of an inch, short, perpendicular, with the distal ex- 
tremity of each very slightly introverted. 
The chief characteristic of this species is afforded by its remarkable 
sutural groove. This is distinctly angulated, running in zig-zag straight lines 
from side to side. From the outer point of each angulation a short horizontal 
groove continuous with that of the suture traverses the covering of the 
coenosarcal tube almost to its outer edge. 
This form has been frequently figured by palaeontologists, even under its 
most typical aspect, but always in association with closely allied forms. (1) Its 
characters are so unique that there can be no hesitation in regarding it as a 
distinct species. 
The various forms here referred to C. Scalaris. His. universally 
abound in Bala and Lower Llandovery rocks. They are unknown apparently 
in rocks of Llandeilo and Lower Bala age, where their place is taken by the 
present species, which occurs in Wales, Scotland, and Scandinavia in these 
ancient formations. The two forms doubtfully overlap for a short period in 
the Clingaili zone of the Hartfell shales of the Moffat area. Localities-Scot- 
land— in the Glenkiln and lowest Hartfell beds everywhere. Ireland— Bally- 
grot, Craigavad, and Coalpit Bay. 
65. Sp. 3. Climacograptus bicornis. Hall. Type form. PI. 6, fig. 38a. 
Locality — Ballygrot. 
66. Var. (b.) tridentatus. Lapw. PI. 6, fig. 38c. 
67. Var. (c.) peltifer . Lapw. PI. 6, fig. 38b. 
68. Sp. 4. Climacograptus ccelatus . Lapw. PI. 6, fig. 39. 
The figure which illustrates the original description of this species (Quart 
Journ. Geol. Soc., 1875, PI. 35, fig. 8) is a very bad one. The original 
diagnosis should be compared with the figure on plate of the present memoir. 
In the Welsh specimens the hydrothecae are more deeply divided and the” 
(1) Compare, for example, Boch, Bernerk aug., Graptolitherne, Taf. 1, figs 3 ro „ l8 
Scharenburg, Ueber Graptolithen, Taf. 2, figs. 24, 25, &c , &c. Salter Q. J. G. S vol viii ’ 
pl- 7 . fig. 3. Torquist. ‘ '* 
L 
