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 thecae 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, 11 1.) 



According to Professor Hall, the polypary in this genus has no central 

 septum, and the hydrothecse are simple openings in the outer test of a single 

 internal ccenosarcal 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 virgulae 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 hydrothecae of both series 

 open into one and the same central ccenosarcal canal. 



58. Sp. I. Climacograptus scalaris. His. (Non Linnaeus.) (Lethea 

 Suecica, Plate xxxviii.) 



The form figured by Linnaeus as Graptolilhus 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 Monograptus, 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, 

 j Skanska Resa., p. 147. 



