OF LOWER GREENSAN'I) PLANTS. 49 



which measure apparently only 1-5 up to 2 crn. in diameter, 

 while those of B. Gibsonianus measure 2*5 up to 3 cm. Another 

 noticeable feature in which this plant differs from the only 

 described British Lower Greensand form, is in the relative 

 massiveness of the trunk and the leaf-bases. In the new 

 species, where the trunk measures 21 cm. in diameter, the 

 leaf-base thickness is only 3 cm. ; but in B. Gibsonianus, with a 

 trunk only 28 cm. in diameter, the leaf-bases account for about 

 7-10 cm. in the total diameter. 



These differences are sufficient to indicate that we are dealing 

 with a species different from B. Gribsonianus. Without the 

 internal anatomy absolute certainty cannot be reached, but it 

 seems to be a new species. 



So far as I can judge, the specimen described by Capellini 

 and Solms-Laubach (1892, p. 207) Under the name Cycadeoidea 

 Capelliniana, Solms, seems to approach it nearer than the other 

 forms in the shape, size, and appearance of the leaf-bases. 

 The only indications given in their figures of the cones in this 

 species, however, make them out to be much larger than in the 

 British specimen ; while this may not be a true specific character, 

 and may be due only to differences in age, it is a point that 

 cannot be determined with the available material. 



From the much older rocks of Portland, Buckland described 

 a species named by him Cijcadeoidea micropltylla. The plant he 

 figures (Buckland, 1828 A, pi. xlix) is very much larger than our 

 specimen (measuring, according to his illustration, 45 cm. in 

 diameter), and the size of the individual leaf-bases also is greater. 

 In the Museum there are now a number of Portland specimens 

 labelled with this specific name, several of them much smaller 

 than the type, but even in these the leaf-bases are distinctly 

 larger than in our new form, and measure commonly over 2 cm. 

 in tangential diameter ; Buckland gives the si/.e as 1 in. 

 (2-5 cm.). (See also Appendix.) 



As the difference in age between the plants is so great, 

 I should in any case hesitate to place them in the same species 

 without definite characters being determinable in each (see 

 also Appendix, p. 295). I therefore name the new species after 

 Mr. Allchin, the Curator of the Maidstone Museum, in which 

 the type-specimen is preserved, to whom we are indebted for 

 opportunities of studying and taking a cast of it. 







