34 THE VICTORIAN NATURALIST. [Vol. XXIV. 



It is situated at an elevation of 3,100 ft. above sea level, with the 

 north-west knob of Mt. Wellington rising 2,000 feet above it (on 

 the right). The rocks from the lake level to the top of the 

 plateau consist of porphyritic rhyolites. For theories as to the 

 origin of the lake see Victorian Naturalist, vol. xxii., p. 22. 



No. 2. — View of the Wellington valley, looking west from the 

 Monument Gap, showing the Serpentine area, with the Crinoline 

 Mountain in the distance. The remnant of the plateau character 

 is shown by the near bluff on the left. Two fault scarps show in 

 the Wellington valley to the right of the centre of the picture. 

 The transverse valley in the foreground is that of the Dolodrook. 

 The nearest hill on the right consists of Ordovician slates. The 

 rest of the ranges consists of Upper Palaeozoic rocks. 



[The paper was illustrated by a large series of lantern slides. — 

 Ed. Vict. Nat.] 



On Some Fossils from Silurian Limestone, Dolodrook 

 Valley, Mt. Wellington, Victoria. 



By F. Chapman, A.L.S. 



Platystrophia biforata, Schlotheim (sp.) 



The present examples are very variable, both in size and 

 external characters. The costate ornament passes from the 

 typical stoutly ribbed form figured by Schlotheim into the more 

 finely costate shell exemplified in some British fossils from the 

 Wenlock Series. One at least of these specimens further varies 

 in having bifurcated ribs, after the manner of M'Coy's var. fissi- 

 costa, from the Ordovician of the Chair of Kildare, Ireland, but 

 with a greater divergence. 



This species has a wide geological as well as a geographical 

 range, extending from the Ordovician (Bala Series) to the 

 Wenlock in Great Britain and North America. It is also found 

 in the Silurian of Europe generally. By the occurrence of 

 Plati/strophia biforata in the Silurian (Yeringian) beds of North 

 Gippsland, it is evident that the species survived longest in this 

 area of the world, so far as at present known. 



Crinoid stems, indet. — Fairly numerous. 



Pellets of encrusting organisms. — These form a large part of 

 some of the limestones, perhaps as much as 40 or 50 per cent., 

 but their intimate structure has been entirely removed by secondary 

 crystallization, and only traces of their concentric mode of growth 

 can be seen, together with a nucleus of a shell-fragment or crinoid 

 joint. 



Similar concentrically structured limestones (pisolite) are also 

 found in the Ordovician of Girvan, Scotland, and of Wenlock, 

 England, as well as in the Island of Gotland. These pisolites 

 owe their origin to an encrusting organism called Girvanella. 



