146 TABULATE CORALS. 



discoidal form ; the rounded tubercles which they carry upon 

 their surface, as well as the rods which connect contiguous 

 columns, are casts of the mural pores, left by the solution of the 

 thick walls ; and the vertical ridges (not always present) are 

 casts of the grooves between the septal ridges or striae. More- 

 over, perfect examples of P. problematicuin show that the cor- 

 allum was concavo-convex, its under surface being concave 

 (probably a character of specific value), and covered by a con- 

 centrically-striated epithecal membrane. So far there is no 

 difficulty in interpreting the peculiarities of the P. problemati- 

 cum of the European Devonian by the light afforded by the 

 well-preserved coralla of allied forms in the corresponding forma- 

 tion in North America ; but there remain two points of difficult 

 interpretation. One of these points consists in the occasional 

 existence of numerous small pits — much more numerous than 

 the corallites themselves — on the upper surface of the cast of 

 the epitheca (see Pol. Foss. des Terr. Pal., PI. XVIII., figs. 4 

 and 4 a). Messrs Meek and Worthen have not only noticed 

 the same phenomenon in the American specimens, which they 

 provisionally refer to P. problematiczLm, Goldf. ; but they notice, 

 in addition, that the corallites which rest directly upon the 

 epitheca are connected with the latter by rods precisely similar 

 to those which unite the different corallites with one another. 

 They suggest that this indicates the occurrence of " pores " 

 passing through the base ; but it may be offered as a probable 

 explanation that these really indicate the existence in this 

 particular species of numerous radiciform and hollow pro- 

 longations of the lower surface of the epitheca, such as 

 are known to occur in Michelmia favosa, Goldf, and which, 

 after all, are essentially of the same nature as the "mural 

 pores." 



The other point of difficulty consists in the presence in many 

 (but apparently not in all) specimens of P. problematicum, 

 Goldf, of the curious structure known as the "vermiform 

 body." This body (fig. 22, a) has the form of a cylindrical, 

 crooked, often S -shaped rod, occupying the centre of the base 



