Silurian.-] PALEONTOLOGY OF VICTORIA. ITrilobites. 



Description. — Head semi-elliptical, pointed, with a slig-htly upturned edge in 

 front, deflexed at the sides to the rounded posterior lateral angles, leavino- the cheeks 

 moderateh" convex ; glabella scarcely defined, slightly convex at base, surface slightly 

 concave between it and front margin ; eyes moderate. Thoracic rings continuously 

 arched across the back, rather abruptly deflected near outer ends, each divided by 

 a fine impressed sulcus midway between the anterior and posterior edges. Pygidium 

 very distinctly trilobate ; axis convex, defined by sharp longitudinal sulci on each 

 side. Segments distinctly marked (number uncertain, and the shape of apex, from 

 imperfection of specimen). Length of head, 10 lines ; width at base, 1 inch 4 lines ; 

 length of thorax, 1 inch 3 lines ; width of front of pygidium, Uplines; width of 

 axis, (3 lines. 



This highly typical species of Homalonotus was first discovered 

 by one of our valued scientific men, whose retiring disposition will 

 scarcely permit me the pleasure of naming after him the most remark- 

 able trilobite yet found in Australia. Mr. T. Harrison was so kind as 

 to present the specimen to the Museum directly he knocked it out 

 from the sandy beds in the Royal Park, near Melbourne, to which, 

 from other fossils, I had assigned an Upper Silurian age on first 

 landing in the colony. It is to be distinguished from the Homalo- 

 notus delphinocephalus (Green) of the Upper Silurian rocks of 

 North America, to which it is most nearly allied, by the total 

 absence of even the slightest trace of trilobation of the rings of 

 the thorax, and by the sulcus which divides each of them being in 

 the middle so as to divide each thoracic ring into two nearly equal 

 portions ; while in the H. delphinocephalus there is a slight 

 depression on each side where the axal furrows are in ordinary 

 trilobites, and in it the anterior portion of each segment is very 

 much narrower than the posterior division, from the sulcus being 

 close to the anterior edge. The apex of the pygidium is un- 

 fortunately broken in our specimen, so that the precise form of that 

 part is as yet unknown. 



Rare in sandy U])per Silurian (May Hill Sandstone) strata near 

 Flemington, north of Melboiu-ne. 



Explanation of Pigures. 

 Plate XXIII. — Fig. 11, natural size of nearly perfect specimen, the posterior part of the 

 pygidium only being absent. 



Frederick McCoy. 



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