56 GEOLOGICAL MEMOIRS. 



for in simple-ribbed Spirifers an incipient dichotomy very often ap- 

 pears in the sinus. Yet a division so strongly marked as that of the 

 ribs of Spirifer Keilhavii must be sufficient to establish a peculiar 

 species. It does not appear so distinct and with so few ribs on the 

 Spirifers of other regions, although related forms are easily found. 

 Singularly enough, those with the greatest degree of similarity occur 

 at the distance of the whole diameter of the globe from Bear Island, 

 in Van Diemen's Land and the interior valleys of New South 

 Wales. 



Spirifer Tasmanni was brought to London along with many 

 others by Count Strzelecki, and is described in his instructive work 

 (Physical Description of New South Wales and Van Diemen's Land, 

 250) by the cautious and experienced palaeontologist Mr. Morris, in 

 London, and figured (pi. 15. fig. 2). It had, however, been de- 

 posited in the Royal Mineral Collection (Berlin) many years pre- 

 viously by M. von Dechen, and, singularly, under the same name that 

 Mr. Morris has given it. It has many more, and hence smaller ribs, 

 than the Spirifer Keilhavii, at least ten on each side, and the ribs are 

 likewise bifurcated from the middle, or more commonly divided into 

 three, two smaller on each side of the larger rib in the middle. The 

 sinus and lobe (Wulst) are in it also covered with the finer ribs only, 

 and a great part of the area is concealed under the curved-over 

 beak. 



Spirifer Stokesi (Strzelecki, pi. 15. fig. 1) would come nearer 

 to the Sp. Keilhavii, were not the external form too distinct. For 

 the sides of the shell converge towards the front, instead of being 

 vertical, and the ventral valve rises considerably higher than the 

 dorsal, and with more decided convexity. Otherwise there are in 

 like manner six broader ribs on each side of the sinus, which divide 

 into three distinct ribs. It is also found in Van Diemen's Land, and 

 belongs to the carboniferous formation. 



As Van Diemen's Land, the most southern promontory of the great 

 continent of New Holland, terminates in formations full of Spirifers, 

 this phsenomenon is in like manner repeated on the promontories, so 

 similarly formed, of Africa and South America. There also the beds, 

 with which these quarters of the globe end, are especially characterized 

 by species of Spirifers, thus proving that in them also the oldest 

 strata known to us crop out, whilst on the other hand newer forma- 

 tions are rare in the southern hemisphere, and almost limited to the 

 northern continents. The Spirifers, however, both of Cape Horn and 

 the Falkland Islands, as well as those of the Cape of Good Hope, 

 belong to the older Silurian strata, far removed from the coal forma- 

 tion, and not to the carboniferous limestone, like those found in the 

 vicinity of Hobart Town in Van Diemen's Land. Hence these species 

 of Spirifers are no longer covered with divided, but only with simple 

 ribs. On Hokmans Kloof in Zwellendam, at the Cape, M. Kraus of 

 Stuttgart, the no less bold than enterprising naturalist to whom we 

 owe so many new and important discoveries in Port Natal, has 

 discovered a whole stratum almost composed of such Spirifers. It 

 is one of the largest species. 



