Lapworth- Graptolites of Co. Down. 137 
leave indubitable traces of its presence upon the matrix. Locality — 
Coalpit Bay. 
57. Var. obesus. Lapw. (Rept. Brit. Assoc. 1871.) PI. 6, fig. 29. 
The special features of this form are the great size and the elegant and cha- 
racteristic shape of the thecal meshes. The thecse themelves appear almost 
horizontal. Locality — Unknown in Ireland ; common in the Gala Group of 
South Scotland, and in the highest seams of the Birkhill shales. 
Genus X. Climacograptus. Hall. (Grapt. Quebec Group, p, hi.) 
According to Professor Hall, the polypary in this genus has no central 
septum, and the hydrothecae are simple openings in the outer test of a single 
internal coenosarcal canal. By Professor Nicholson, on the other hand, the 
polypary is believed to be formed, actually or theoretically, of two monoprio- 
nidian polyparies placed back to back ; their dorsal walls being flattened into a 
bilaminate median septum, and their virgulse coalescing into a double central 
virgula. I have verified the accuracy of the latter theory in the species 
Climacograptus scalaris (His.), in several of its varieties, and in C. Wilsoni. 
(Lapw.) ; but if the analogy furnished by the structure of Diplograptus as 
described above, is to guide us, it is not impossible that both these interpreta- 
tions are correct, each for itself, and that within the limits of Climacograptus , as 
at present received, are included some forms in which the median septum is con- 
tinuous from side to side, and others in which the hydrothecas of both series 
open into one and the same central coenosarcal canal. 
58. Sp. 1. Climacograptus scalaris. His. (Non Linnaeus.) (Lethea 
Suecica, Plate xxxviii.) 
The form figured by Linnaeus as Graptoliihus scalaris, (1) was a Monograptus 
allied to M. colonus of Barrande, from the Upper Silurian strata in which the 
genus Climacograptus is unknown. Examples in my possession procured from 
the same locality whence Linnaeus obtained his species show the peculiar scala- 
riform appearance figured by him, with great distinctness. They are also asso- 
ciated with unrolled examples of a spiralis like Cyrtograptus , as in his original 
drawing. Linnaeus’ name, scalaris , should be employed for the Monographs, to 
which he originally applied it; but in the meantime it is perhaps inadvisable to 
disturb Hisinger’s title for the Swedish Climacograptus. The following forms, 
1 Skanska Resa., p. 147. 
