314 Notices of Memoirs — A Fossil Cycad, Portland. 



^^Cycad 



y7rP/f'r-/f lYr 



^hijLinq ruLZle 

 Top. slate 

 Shaley Cla^ 

 ShiTighLed 

 Soft slaty stone 

 iSeam of clau 



Geologists have long been familiar with the short and thick 

 Cycadean stems described by Buckland and others from the Purbeck 

 beds of Portland, but the recently acquired fossil differs in many 

 respects from the shorter stems or " crows' nests " hitherto recorded 

 as the common type of Cycads from this locality. The specimen 

 ^^,, was found in one of Mr. Barnes' quarries, 



and, as shown in Fig. 1, it was obtained 

 from a bed of shaly clay 17 feet higher 

 in the Purbeck series than the Great 

 Dirt-bed which has yielded most of the 

 Portland plants. Mr. A. M. Wallis, 

 a local guide and quarryman, who at 

 once recognized the value of the speci- 

 men, saved it from destruction, and Dr. 

 Woodward was fortunate enough to ob- 

 Hard. slate ted tain the magnificent stem for the National 

 Collection. 



The trunk is shown in its natural 

 position in Plate XIII, which is repro- 

 duced from a photograph taken by Mr. 

 Gepp of the British Museum. The total 

 height is nearly four feet (1 m. 18*5 cm.), 

 and the girth at the broadest part about 

 1 m. 7 cm. The surface features are best 



_ seen close to the base (Plate XIV, Fig. 2) ; 



l \^\ '^M^ j) ■^g^^ f'^P there is a prominent network with meshes 



arranged in regular rows and passing 

 spirally round the stem. Each mesh 

 marks the position of a leaf-stalk base ; 



^ , c j^. i. -T. the substance of the petiole has dis- 



FiG. 1. — Section of the quarry , . . tip. -l 



on Portland in Avhich the Cyca- appeared m most cases and left a cavity ; 

 dean Stem was discovered by Mr. the reticulum consists of ridges of 

 A. M. Wallis. silicified tissue, which existed between 



the individual petioles. In the living plant numerous scaly or 

 laminar appendages were attached to the surface of the petiole 

 base, and these formed a kind of loose packing between the 

 fronds. The chaffy scales or pale^ on the leaf-stalks of many 

 recent ferns are almost identical structures, and among existing 

 Cycads somewhat similar appendages are occasionally met with. 

 The mineralizing solution was apparently absorbed more readily 

 by the interpetiolar tissue than by the less porous petioles ; the 

 former was therefore more frequently preserved, and in a better 

 condition than the latter. 



At the top of the stem an apical bud has been clearly preserved. 

 It is very unusual to find fossil Cycadean stems in which the apical 

 portion has been left intact. The bud is covered with numerous 

 bud-scales, and at the summit there is a terminal cap, shown in 

 Plate XIY, Fig. 1, as a lighter-coloured patch. In Fig. 2, p. 319, 

 this cap presents the appearance of a mass of numerous fine hairs 

 covering the tips of the linear bud-scales. 



-Wilftedi'^'Rfi'ac. 

 HbrtlaJid'beds 



