CORALS FROM THE SILURIAN FORMATION. 299 
Protovirgularia dichotoma,’ may probably belong to the group of Sertularina, the other, 
Pyritonema fasciculus,” is a cylindrical bundle of small vertical tubes. 
1 Ann. and Mag. of Nat. Hist., 2d ser., vol. vi, p. 272, 1850; Brit. Palooz. Foss., p. 10, pl. i, 
figs. 1] and 12, 1851. 
“One specimen, about two and a half inches long, branches twice at an angle of about 30°, and 
shows all the pinnules extended at right angles to the capillary axis, with a gentle upward curvature, like 
the living Virgularia in the same state; another simple fragment about the same length has them half 
extended, being nearly straight, and oblique to the axis; a third fragment has them quite contracted, re- 
sembling a bit of narrow braid, exactly like the contracted state of the recent Mirgularia mirabilis. This 
one shows very plainly the transverse cell-ridging. Width rather less than one line; four pinnae in the 
space of two lines. 
“Tn the slate at Roekerby, Dumfriesshire.” (M‘Coy, loc. cit.) 
2 Ann. and Mag. of Nat, Hist., 2d ser., vol. vi, p. 2738, 1850; Brit. Paleeoz, Foss. p. 10, pl.is, 
fig. 13, 
“1 have proposed the above name for a singular fragment of a fossil from the dark limestone of Tre 
Gil, S. of Llandeilo. It is nearly straight, about two anda half inches long, four lines wide, and one and 
ahalf line thick, and marked longitudinally with coarse thread-like ridges, about the third of a line in 
diameter, occasionally cut by small sharp transverse wrinkles; the whole having some resemblance to an 
Iehthyodorulite (onchus or ctenacanthus). On first seeing the specimen, [ doubted this reference, from 
observing that the ridges, instead of being merely superficial, thicker, and more numerous at one end, as 
they should be on this view, seemed equally thick at each end, and clearly not in one plane, but those at 
the surface of one part plunging into the mass and giving place to others emerging from it. Owing to the 
skill and kindness of Mr. Anthony, of Caius College, two sections for the microscope were prepared, which 
proved that the whole mass was really a bundle of thread-like rods of silica, corresponding exactly in 
diameter with the external ridges, the sections of which exactly correspond with the others in the interior ; 
the siliceous fibres are solid, cylindrical, with slight occasional transverse rugosities ; they are less than 
their own diameter apart, and the interstices shew no organisation under a magnifying power of 300 diameters, 
the limestone being of a finer texture, and lighter colour than that of the matrix, as if there had been 
originally a soft animal matter in the spaces between, which kept out the coarse calcareous mud, but the 
space occupied by which became filled with fine material by percolation on its decomposition.” (M‘Coy, 
loc, cit.) 
