556 STUDIES IN FOSSIL BOTANY 



limited a group. The Cycadophyta, in fact, were as 

 characteristic of Mesozoic vegetation as are the 

 Dicotyledons of our present Flora. Among the 

 commonest remains are leaves, which in many cases 

 closely simulate those of existing Cycadaceous genera, 

 and have hence received the names Zamites, Dioonites, 

 and Cycadites. These generic resemblances, however, 

 are usually deceptive ; the Zamites and Dioonites 

 leaves are now known to have belonged to plants 

 which had only a somewhat distant affinity with the 

 Order Cycadaceae, while in certain leaves once referred 

 to Cycadites, or even to Cycas itself, the similarity to 

 those of the recent genus has proved to be illusory 

 (see below, p. 595). In other leaf-genera, again, such 

 as Otozamites and Anomozamites, the foliage, while of 

 a Cycadean type, differs evidently from that of any 

 of the existing genera. 1 



In addition to the leaves, fossil trunks, which 

 present the external characters of Cycadean stems, 

 are of common occurrence in the older Secondary 

 rocks, as, for instance, in the Wealden of Sussex and 

 in the well-known " dirt-bed " of the Lower Purbeck 

 strata in the Isle of Portland, and at other places 

 along the Dorsetshire coast. The stems are usually 

 short, though they may appear shorter than they 

 actually were, owing to pressure of the superincumbent 

 strata. The surface is usually covered by the closely- 

 set bases of the leaves ; the upper end of the stem is 

 commonly hollowed out, owing to the decay of the 

 growing apex. " Fossil crows' nests " is the name by 



1 Numerous figures of the leaves of Mesozoic Cycadophyta will be 

 found in Seward's Catalogue of the Mesozoic Plants in the Department of 

 Geology, British Museum, Parts ii.-iv. 1895- 1904. 



