70 MR. STANLEY SMITH ON [Harch 1913, 



column, and form with the central vesicles the retiform design 

 seen in PL VIII, fig. 3. A specimen from Bristol seems to show a 

 little advance upon the Tenby specimens, but it is too fragmentary 

 and too ill-preserved to afford reliable information. Tbe adult 

 character of the central column is that of Stage 1) of A. fimgites 

 mut. cumbriense. 



Both these early forms of Aidophyllum are rare. 



(4) Forms from the Middle and Upper Dibunophyllum 

 Zones (D 2 -D 3 ). 



A. fungites mut. yachyendothecum is distinguished by 

 the great number of principal septal lamellae. Between mutations 

 redesdalense and pachyendothecum come a series of passage-forms 

 equivalent to Stage E. These intermediate mutations mark a 

 distinct stage in the phylogenetic history of the genus, but will be 

 referred to as ' mutations towards pachyendothecum.' 



A. fungites mut. cumbriense retains in the adult the 

 retiform design of the D 1 mutation tenbiense, but in an intensified 

 degree (PI. VIII, figs. 1 & 2). This form is typical of the southern 

 areas, 1 and I have not seen an example from the northern localities.- 

 At Stage D the characters are those of mut. tenbiense. 



Prom the character of the central column of Stage D (PI. VIII,. 

 fig. 4), see pp. 64-65, it would seem in most cases that those forms 

 which are found in northern areas were descended from mut. 

 redesdalense ; while the forms found in the more southern areas 

 (all the forms of mut. cumbriense and many forms of pachyendo- 

 thecum : PI. VIII, fig. 6 a) had been evolved from mut. tenbiense. 

 In Stage D of some individuals the character of the column is 

 intermediate between the above-mentioned types. These may have 

 descended from one or the other of the D 1 mutations, or possibly 

 from some intermediate form. 



One cannot always say whether the section nearest the calyx of 

 a particular individual represents the highest stage of evolution 

 possible for it to have attained. To prove a stage as final, it is 

 necessary to show its persistency throughout the cylindrical portion 

 of the corallum ; this cannot be done in the case of conical and 

 imperfect specimens. 



VIII. Local Characteristics and Variations. 



Although the characters of the D.,-D. 3 forms have been fully 

 treated, it still remains to survey briefly the material obtained from 

 some of the different localities, and to remark upon one or two 

 local types. 



(a) Bathgate. — Much has already been said concerning the 



1 The Craven district, the country around Morecambe Bay, and the Carbon- 

 iferous Limestone areas south of these localities : that is, North and South 

 Wales, Bristol, etc. 



3 Northumberland, Durham, and North Yorkshire. 



