STOMATOPOR^ AND ASCODICTYA. 



615 



possible that Lonsdale and other workers on the Silurian organisms 

 may have had a prerious knowledge of the fact of their existence in 

 these rocks ; but no detailed account was furnished. For the work- 

 ing-out of these and other forms of Stomatopora we are equally in- 

 debted to Prof. Nicholson, M.D., F.G.S., &c. 



Silurian Stomatoporce. 



1. SXOITATOPOEA IXTLATA. 



AJecto inflate, Hall, Pakeont. of Xew York, vol. i. p. 77, pi. xxvi. 

 figs. 7(7. b. = Hippothoa inflata, Xicholson, Ann. & Mag. Nat. Hist. 

 Feb. 1S75, pi. xi. figs. 1. la. 



" Zoarium* attached, arachnoid : zocecia short, much expanded 

 above, contracting at the aperture and narrowing rapidly below : 

 orifice large, opening obliquely upwards." 



This is Hall's description of his species. Xicholson says that the 

 branches of his specimens are linear, and the " cells uniserial and 

 pyriform. each springing by a contracted base directly from the cell 

 below : about four cells in the space of one line.*' There is nothing, 

 however, in his description that would ally the species with the 

 Hippoihoa : but in working out my own TTpper-Silurian types I have 

 given prominence to every feature that had any tendency to a Hippo- 

 thooid character. 



The geological position of Hall's species is the Trenton Limestone. 

 Nicholson's specimens are from the Hudson-River Formation, Cin- 

 cinnati Group. 



2. Stoitatopoea dissimixis. mihi. Figs. 1-8 (p. 616\ 



Zoarium adnate, branching, generally attached to stems of Cri- 

 noidea. very rarely to broken shells : branches linear, sometimes 

 wavy and anastomosing. Zocecia invariably uniserial, and, in the 

 best preserved, very finely ribbed transversely ; the oral extremity 

 slightly raised ; orifice circular or snbcircular. Oceeicd cells rather 

 ventricose and strongly ribbed (?). Each normal zocecium about 

 half a line ; average about 6 to 3i lines. 



Loc. Fpper Silurian ; *• Buildwass beds,'' Harley, near Wenlock, 

 rather rare : also base of Wenlock shale, Buildwass Bridge. Shrop- 

 shire, rather common. 



I have not found any specimens of this species in any other of 

 the eleven localities which I have searched for Polyzoa. In search- 

 ing the material from these two localities, I found it to my interest 

 to examine on both sides every fragment of shell and Crinoid that 

 came under my glass ; the consequence of this is that I have speci- 

 mens, more or less perfect, of about fifty colonies. The drawings 

 are made from three of these, because they afforded me better facies 

 than the others. What I have given are characteristic of the 

 whole. 



* To present a uniformity in the descriptions, I change the exact words of 

 authors to those in present use : thus. Hall's word iS Coral " is changed to Zo- 

 arium, " Polvzoary " of authors to the same. 



