Si/unan.] PALiEONTOLOGY OF VICTORIA. \_Trilobites. 



anterior seg-mental furrow to basal ftirrow, conico-reniform very prominent, with 

 coarse lenses about 8 to 13 in a vertical row, usually 10. i«J?7(??) about 8 lines 

 long', and the same in width, anterior margin of which is arched like the front of the 

 g'labella, only alig-htly convex ; a deep furrow within the lateral margins forms a 

 shorter semi-ellipse below than the outer edges, which are nearly straight and parallel 

 at the sides, but form a rounded tongue-shaped lobe extending 1 J lines beyond the 

 inner furrow (edge denticles not visible), an oblirpie pit on each side a little within 

 the anterior curve of the furrow. Tlwrax mid-lobe convex, outer ends of segments 

 tumid ; lateral lobes, about J wider than the axis, much curved down at the sides, 

 very finely granulose. Pygidhim semi-ellipitical or sub-trig-onal, undivided side 

 margins slightly convex, converging at a little more or less than a right-ang'le to a 

 flat triangular more or less elongate posterior spine; axis moderate convex, g-radually 

 tapering-, and composed of 12 distinct ribs (and sometimes 3 or 4 small indistinct 

 additional at tip), often tumid at outer ends ; lateral ribs 9, prominent, arched down- 

 wards and backwards at the ends, each divided by an impressed groove throughout 

 its length. Surface of thorax and pygidium closely covered with a fine unequal 

 granidation. Average length of head and of pygidium about 1 inch. 



Referknce. — Trilobus caudatus (Briinnich) Kjobenh. Sellsk. Skrifter. Nye. 

 Samml. v. 1, p. 392 = Asaphus caudatus (Bsong.) Crust. Foss. t. 2, f. 4. Murch. 

 Sil. Syst. t. 7., f. 8. 



Of all the fossils of the Palaeozoic rocks, the Trilobites are 

 undoubtedly the most characteristic and interesting, and to find the 

 commonest species of the English Ludlow and Wenlock rocks, and 

 most characteristic Upper Silurian fossil equally common in the 

 rocks of the same age in Australia, and to he able to show by the 

 accompanying figures that the Welsh and Victorian individuals 

 present exactly the same range of variations, is a great pleasure to 

 me, as I am sure it will be a surprise to geologists. This is all the ' 

 more extraordinary as the most abundant Trilobite genus charac- 

 teristic of the Lower Silurian of every part of Europe and America 

 — Trinucleus — has not yet occurred to me in Australia, where I 

 have jiroved the wide-spread existence of the latter rocks by so 

 many European and American species of Graptolites. 



Although the number of axal segments in the p3'gidium is given 

 above as greater than in the English descriptions of this species, 

 I have covmted precisely the same number in British as in the 

 Australian specimens, the difference depending on the distinctness 

 or not, and counting or not, of the last few very small rings 

 represented in the figures in Decade 2, Plate 1, of the English 

 Geological Survey. The same variations in the width or narrow- 

 ness of the pygidium, and the length or shortness of the posterior 

 spine occur in the Australian as in the English examples, as shown 



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