THE VICTORIAN NATURALIST. 



is not usually so straight as in the specimen before me, being 

 slightly curved, and hence not so suggestive of Glossopteris, but 

 sufficiently well marked to show that a decided median sulcus is 

 sometimes found in the Bacchus Marsh leaves, and more often in 

 those of the spatulate type. 



Although this groove does not partake of the character of a 

 distinct midrib, yet it is seen to be formed of a series of greatly- 

 thickened veins, starting from near the petiolate end, and running 

 nearly parallel as far as the sulcus extends. The sulcus never 

 occurs actually at the base of the leaf as in Glossopteris, and 

 is strongest in the median area. Sometimes, as in the present 

 specimen, it is persistent to the apex. 



The measurements of our specimen are : — Length of leaf, 

 50 mm. ; greatest width (at 32 mm. from the base), 24 mm. ; 

 width of median sulcus at widest point, about 1.25 mm. ; 

 the angle of divergence of lateral veins from the median sulcus, 



I5°-20°. 



Conclusions. — The reasons for believing this example to be 

 merely an abnormal type of Gangamopteris, whilst bearing in 

 mind, however, the several points of relationship between the two 

 genera, are : — 



1. The sulcus is not persistent throughout the length of the 

 leaf. 



2. The lateral margins of the sulcus are not so clearly defined 

 from the area bearing the lateral veins as in a typical Glossopteris 

 leaf. 



3. Other examples of leaves with a similar median fold, 

 although not so regularly disposed, occur in the same beds at 

 Bacchus Marsh, which are undoubtedly examples of Gangamop- 

 teris as we at present attempt to define the genus. 



On the other hand, it is only required that the median veins 

 become locally fasciculate and persistent throughout the length 

 of the leaf to resemble the Glossopteris type ; and evidence of 

 such a modification with intermediate characters seems to exist 

 in Glossopteris gangaTnopteroides. 



There is, by the way, nothing of the conspicuous net-venation 

 in our specimen which would justify its reference to the genus 

 Sagenopteris, a form which also possesses a fine mid-rib. 



Judging by the figures given by Johnston * of immature leaves 

 of Gangamopteris, it would appear that forms such as the present 

 are of not rare occurrence in Tasaiania. In Johnston's examples, 

 however, the median fold seems remarkably well defined near the 

 base of the leaf, as compared with similar small Victorian 

 examples in the National Museum collection. 



In view of the close relationship between the two genera 



* Geol. Tasmania, 1888, plate x., figs. 4-8. 



