CYCADEAE, MEDULLOSEAE. 99 



branch before they reach the leaf-stalks, and there is therefore no ap- 

 pearance of the leaf-trace-girdles which characterise our recent Cycadeae. 

 How far this is true of all stems of Bennettites will have to be determined. 

 Essentially the same characters as those of Bennettites are presented 

 by a series of forms which compose Carruthers' genus Mantellia, and 

 which were named by Buckland Cycadoidea. The only differences adduced 

 are the lesser height, the globular or tuber-like shape, the circular outline 

 of the transverse section, and the circumstance that the fertile shoots 

 project above the armour of scales and have only their basal portions 

 preserved ; the latter character however, even if it were of universal 

 occurrence, which I doubt, cannot be looked upon as in any way essential. 

 To these forms belong the remarkable imperfectly silicified stems of low 

 growth, which have their upper extremity hollowed out by decay of the 

 tissue into the form of a bird's nest, and in this state have been found in 

 great numbers in the stone quarries of the Isle of Portland near Weymouth. 

 The Purbeck formation begins in this locality with marine limestones 

 which have supplied the material for many buildings in London ; these 

 are succeeded by a fresh-water or estuarine deposit, at the base of which 

 are two carboniferous earthy layers about a foot in thickness and separated 

 from one another, the so-called dirt-beds, with numerous prostrate or 

 upright silicified stems rooted in them. Among these stems and in like 

 position are found the Cycadeae which are called birds' nests by the 

 labourers, either singly or here and there in groups. For a further account 

 of the matter the reader is referred to Buckland and De la Beche 1 . Figures 

 of the different species distinguishable by the size and form of the scars 

 left by the detached scales are given by Carruthers 2 (Bennettites Port- 

 landicus, Carr., Mantellia nidiformis), by Schimper 3 (Cycadoidea megalo- 

 phylla, Buckl.), and by Buckland 4 (Cycadoidea megalophylla, Buckl., C. 

 microphylla, Buckl.). The commonest species in the dirt-beds is said by 

 authors to be C. microphylla ; Buckland himself may have included 

 different forms in his C. megalophylla, for the figures show important 

 differences. A fresh and connected examination of all these stems would 

 be very desirable. To the same group also belongs a specimen named by 

 Carruthers 5 Mantellia inclusa, in which the fertile shoots have perished 

 and dropped out, leaving deep and broad holes in the envelope of scales. 

 And lastly, it seems to me probable from Goppert's 6 figures that his Rau- 

 meriae are really stems of Bennettites. I can positively affirm this of 

 Raumeria Schulziana, which was dug out of the ground in making a canal 

 near Gleiwitz during the last century, now that I have seen the original at 



1 Buckland and de la Beche (2). 2 Carruthers (4), t. 61, and t. 63, f. i. 3 Schimper (1), t. 71, 

 f. ii. See also Buckland, Geol. and Min., t. 60. * Buckland (1), tt. 47, 48, 49. * Carruthers 

 .4), t. 63, f. 3. 6 Gbppert (9). 



H 2 



