the Genus Fistuliporaj M^Coy. 



507 



Fig 4. 



undergone. The autopores are sufficiently large to be distinctlj 



seen with the nalced eye ; this arises in some measure from 



their infilling being of a 



lighter colour than that of the 



walls of the cells, otherwise 



they could hardly be perceived. 



They are oval or subcircular in 



form, the folds (which are plainly 



visible under a 1-incli objective) 



occupying, about one fourth of 



the circumference of the walls 



and always pointing towards 



one of the centres of growth. 



About four of the autopores may 



be contained within the space of 



1 millim. ; a few of a somewhat 



larger size are grouped around 



the " monticules." Mesopores 



as seen in transverse section 



polygonal, very variable in size, 



sometimes equalling that of the 



autopores, sometimes much 



F. nummulina, showiug folds in 

 the autopores. 



smaller. Longitudinal sections show that the autopores are 

 provided with tabulee, which are horizontal or a little curved, 

 and that the mesopores are filled with closely-set tabulae 

 which have produced by their coalescence a vesicular tissue. 



Ohs. The species to which F. lamimuUna is most closely 

 allied is undoubtedly F. crassa. Externally the distinction 

 between the two is very obvious, as appears on looking at the 

 figures (PI. XV. figs, 1, 2), one being of a discoid or flattened 

 shape, and the other branching. In their microscopic charac- 

 ters also the two species are distinct enough ; the autopores in 

 F. nummulina being larger than those of F. crassa^ only four 

 of them being required to fill the space of a millimetre in the 

 former species, while in the latter five must be taken. 



Further, the tabulation of the mesopores is not nearly so 

 dense in F. nummulina as it is in F. crassa^ and its vesicular 

 character is therefore not so strongly marked as it is in that 

 species. 



The present species is not unfrequently met with in the 

 grey and greenish shales of the Wenlock group. The speci- 

 men figured was presented to one of the writers by Mr. W. 

 Madeley, of Dudley, who has for many years collected the 

 fossils of that region with much industry and discrimination. 

 Other specimens referred to in drawing up the foregoing de- 

 scription are from the cabinet of Mr. C. Holcroft, also of 

 Dudley. 



