Victorian Fossil*, Part XVIII. L59 



striae, which are transverse or norma] in the median, bifurcated 

 rib, but in maintaining approximately the same direction on the 

 lateral ribs as on the median rib, the striae are disposed in an 

 increasingly oblique manner as the thoracic region is approached. 

 The interspaces between the pygidial ribs, and even the proximal 

 ends of the ribs, are traversed by microscopic raised striae disposed 

 parallel to the margin of the pygidial shield. 



Dimensions. — Total length, 39.5 mm. ; greatest width at 

 thorax, 35.25 mm. Length of cephalon, including neck-ring, 

 11.25 mm.; length of thorax, 10.25 mm.; length of pygidium, 18 

 mm. Greatest width of pygidium, 3d. 5 mm. Width of thoracic 

 axis, 8 mm. Width of pygidial median ridge, 2.25 mm. 



Observations. — The same quarry from which the above holotype 

 was obtained, has yielded several other, more or less imperfect 

 examples, chiefly pygidia, which I tentatively refer to the same 

 species. They range from the moderate-sized and neatly-ornamented 

 flabellated pygidial specimens, to some nearly of twice the dimen- 

 sions, having a slightly coarser rugose ornament. No distinction 

 can be drawn between them. Differences of size and ornament 

 probably represent, in some cases, sexual features. 



The whole carapace in this species is remarkably short; other- 

 wise it compares rather closely with Barrande's Brontens formosusA 

 The Bohemian species, moreover, differs in its narrower frontal 

 margin to the glabella, and the shallower and broader posterior 

 furrow. 



A related but much longer form is Hawle and Corda's Brouteus 

 oblongvs, 2 with similar ornament; the axial ridge of the pygidium 

 in this species, however, is proportionally smaller. In general 

 form, Hawle and Corda's Bronteus berkeleyanus , 3 from the red 

 limestone of Mnenian, Bohemia (Ff2 of Barrande, or Lower 

 Devonian), is almost identical. It differs in having the axis of the 

 thorax narrower, the pygidial axis expanding terminally, and the 

 median ridge bifurcated to one-third of its length, instead of to 

 more than one-half as in G. greenii. 



In reference to the Devonian aspect of a portion of our Silurian 

 fauna, it is interesting to note that the Bohemian allied species. G . 

 formosus, occurs at Dvoretz, in Lower Devonian strata, of the 

 same group of beds as that containing G. oblongus above mentioned. 



1 Syst. Sil. BohOme, vol. i., 1852, p. 851, pi. xlvi., fig. 14 ; pi. xlvii., figs. 1-5. 



2 Prodrom Monogr. d. bohm. Trilobiten, 1874, p. 60. See also Barrande, Syst. Sil. Boheme, 

 1852, p. 853, pi. xlvii., figs. 1317. 



3 Hawle and Corda, Prod. Mon. Tril., 1847, p. 61, pi. !v„ fig. 34. 



