BARRANDIA. 137 



half way out, but not very near the short spinous angles. The glabella reaches and 

 invades considerably the front margin, so as to leave it very narrow in front ; on the 

 sides it is rather broad. The neck-furrow is indistinct. Labrum as broad as long, 

 obtusely pointed, with strong concentric furrows. 



The thorax, of eight narrow well-defined segments, is not quite so long as either head 

 or tail, which are equal. The axis is well defined, gently convex, not quite two thirds 

 the width of the pleurae. The latter are flat as far as the fulcrum, which is placed half 

 way out, then bent down ; the pleural groove very shallow, except beyond the fulcrum, 

 where it is deeper. 



The tail is rather more than a semicircle, ten lines long by sixteen broad. The axis 

 narrow, and tapering, not reaching quite three quarters the length of the tail (in the 

 smaller Welsh specimens it reaches fully three fourths). It is annulated by six or seven 

 furrows above, the upper one often strongest, the rest faint. The sides of the tail are 

 marked by seven shallow short furrows, which do not reach to the depressed border, and 

 the upper one of these also is the strongest. The broad margin is flat or slightly 

 concave. The incurved fascia is very broad, folding over the tip of the axis, and closely 

 striated. Young specimens (fig. 3) show fewer jibs to the axis and sides, and the upper 

 lateral furrow is stronger in proportion. 



Localities.- — ^Arenig group. — Hengwrt Uchaf, four miles north of Dolgelly. (Wood- 

 wardiau Museum, woodcut fig. 31) : Llanfaelrhys, Aberdaron, PI. XVII, fig. 3 (Museum 

 Pract. Geology) ; plentiful at White Grit Mine, near Shelve, Shropshire, figs. 1, 2, 4 to 7 

 (Mus. Pract. Geology ; and Mr. Lightbody's cabinet) ; Mytton Dingle, Stiper Stones, 

 abundant (Mr. Homfray's cabinet). 



Barrandia, MCoy, 1849. 



A group of well-marked species, characteristic of the Llandeilo Flags. The three 

 forms known have the habit of Ogygia, but differ in such obvious characters, that there 

 can be no doubt Prof. M'Coy was correct in separating the typical species B. Corded as a 

 distinct genus. The other two species, here arranged under Barrandia, are not very closely 

 connected with it ; but I do not wish hastily to give a new generic name to them, though 

 very little doubtful of its propriety. The characters of the glabella, and the position of 

 the fulcrum in the pleurae, are too unlike to render it probable that Homalopteon and 

 Barrandia are merely subgenera. But I shall leave them so for the present. 



This small group is a remarkable one, and tends to render the passage of the Ogygides 

 into the Bronteidse so complete, that we may well hesitate about drawing a line between 

 the two families.^ 



1 But the Llandeilo Flag genera have a tliin crust and a wide expanded shape, and are, moreover, 



