CORALS FROM THE SILURIAN FORMATION. 299 



Protovirgularia dichotoma} may probably belong to the group of Sertularina, the other, 

 Pyriton&ma fasciculus? is a cylindrical bundle of small vertical tubes. 



1 Ann. and Mag. of Nat. Hist., 2d ser., vol. vi, p. 272, 1850; Brit. Palseoz. Foss., p. 10, pi. i b, 

 figs. 11 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 Virgularia mirabilis. This 

 one shows very plainly the transverse cell-ridging. Width rather less than one line ; four pinnae in the 

 space of two lines. 



"In the slate at Rockerby, Dumfriesshire." (M'Coy, loc. cit.) 



2 Ann. and Mag. of Nat. Hist., 2d ser., vol. vi, p. 273, 1850; Brit. Paheoz. Foss. p. 10, pl.iB, 

 fig. 13. 



" I 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 and a half inches long, four lines wide, and one and 

 a half 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 

 Ichthyodorulite (onchus or ctenacanthus). On first seeing the specimen, I 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, 

 poc. cit.) 



