VINE: NOTES OX YOEEDALE POLYZOA. 
91 
the Messrs. Young-, of Glasgow, under the name of Rhahdomeson, 
Young & Young'. Since the pubhcation of the Brit. Assoc. Report, 
Mr. E. 0. Uhich accepted the family, and placed in it the genus 
Rhomhopora^ Meek. Although I am quite wilhng to admit that 
externally, certain species of Rhombopora are almost indistinguishable 
from Rhabdomeson gracile, still Mr. Ulrich says that there is an 
absence of the central rod in the American species. Now this feature 
in R. gracile is most characteristic, and in tlie Tearne Limestone, 
Scotland, where the form is abundant, the rod in vertical sections is 
markedh" conspicuous. Yet notwithstanding" this one character — 
the central rod — I am inclined to admit also that there is much force 
in the further remarks of Mr. Ulrich when he says, " A\"hile sections 
of the two genera (Rhabdomeson and Rhombopora) are .... 
readily distinguished, it is, on the other hand, not nearly so easy to 
separate them by their superficial characters. Indeed, examples of 
Rhombopora 2:fer similes, Ulrich, from the Kaskaskia group of Kentucky 
and Illinois, resembles specimens of Rhabdomeson gracile so closely 
in growth, Zoa?cial apertures, and distribution of spines, that it 
requires no little amount of patience to distinguish them successfully."* 
Under these circumstances, and to avoid the introduction of another 
family name it will be best to divide the group into two sections, 
especially so when we have some of the American Rhombopora, or 
very near allies, in British Carboniferous Rocks. 
Section A. Zoacia attached to a central rod. 
Genus, Rhabdomeson Young & Young-. 
Section B. Zotecia radiating- in all directions from an imaginar}'' axis. 
Genus, Rhombopoka, Meek. 
Section A. 
Genus Rhabdomeson, Young- & Young. 
1874-. Annals and Mag. Nat. Hist., May, p. 337. 
1875. Annals and Mag. >;at. Hist., May, p. 334. 
Zoarium slender, rod-like. Axis a thin calcareous tube to 
which the Zocecia are attached and from which they radiate in all 
directions. 
* E. 0, Ulrich, op. cit. p. 25. 
