516 On the Genus Fistulipora, M^Goy. 



rous and mostly of large size. Longitudinal sections show 

 that the tabula bj which the cavities of the autopores are 

 crossed are placed at irregular distances apart. The diver- 

 gence of the autopores from their centres of growth may also 

 be observed in these sections (fig. 2 c) . 



Ohs. A comparison has already been made between this 

 form and F. irifoliata in treating of the latter. 



Formation and Locality. Appears to be rare in the Wen- 

 lock Shales (Upper Silurian) at Buildwas, Shropshire. 



Note. — In his Hist. Nat. des Coralliaires (vol. i. p. 67, 

 1860) M. Milne-Edwards gives a highly suggestive explana- 

 tion of what he conceives to have been the origin of vesicular 

 tabula. We beg permission to lay before the reader the 

 following translation of it : — 



" According to the known disposition of the soft parts of 

 the polyps it is evident that tlie tabulae should correspond to 

 the spaces left open by the atrophy or the successive retreating 

 of the inferior extremities of the mesenteric folds \lames\^ and 

 the degree of their separation would depend upon the length 

 to which this retreating or atrophy was carried in proportion 

 to the growth of the animal. If this upward movement [of 

 the animal] was effected rapidly and completely in each cell 

 \loge] it would result in the tabula being simple and apart 

 from each other. But if the movement was made little by 

 little in an incomplete and limited manner in the different 

 parts of the cells there would be formed a series of blisters or 

 vesicles, of which the general appearance would be that of a 

 cellular or vesicular tissue." 



EXPLANATION OF THE PLATES. 

 Plate XV, 



Fig. \. Fistulipora crassa, Lonsd. sp. View of corallum in the matrix, 



nat. size. (Coll. Johuson, Dudley.) 

 Fig. 2. FistuUjJora mimmulina, Nich. & Foord. View of upper surface 



of corallum, nat. size. 

 Fig. 2 a. Side view of the same specimen, to show thickness of corallum. 

 Fig. 2 b. Transverse section, enlarged about twenty times. 

 Fig. 2 c. Longitudinal section, similarly enlarged. 

 Fig. 3. Fistulipora muscosa, Nich. & Foord. Transverse section, enlarged 



about twenty times. 

 Fig. 3 a. Longitudinal section, enlarged to the same extent. 



Plate XVL 



Figs. \,\ a. Fistulipora utriculus, Rom. Two examples of the corallum 

 of this species, nat. size. 



