Lapworth — Graptolites of Co. Down. 139 



only. Suture deep, zigzag, having each angle prolonged in a short 

 horizontal groove. Virgula distally prolonged. Hydrothecas 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 

 ccenosarcal 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 Clingani 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. PL 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, PL 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 hydrothecse are more deeply divided and the 



(1) Compare, for example, Boch, Bernerk aug., Graptolitherne, Taf. i, figs. 3, 10, 15, 18. 

 Scharenburg, Ueber Graptolithen, Taf. 2, figs. 24, 25, &c , &c. Salter Q. J. G. S., vol. viii., 

 pi. 7, fig. 3. Torquist. 



L 



