2 78 TABULATE CORALS. 



the second case, the callces are rounded, oval, or subpolygonal, 

 and exhibit thick and rounded margins — reminding us, so far 

 as this particular character goes, of the calices of a Pachypora 

 or a Stenopora. Monticulipora petropolitmia, Pand., and its 

 allies may be taken as exemplifying the former condition ; 

 while yJ/. ramosa, D'Orb., M. maimmdata, D'Orb., M. frondosa, 

 D'Orb., M. Jamesi, Nich., M. tuniida, Phill., and many others, 

 are examples of the latter state of parts. Those forms, more- 

 over, in which the walls are thickened towards the surface are 

 particularly liable to exhibit a feature, sometimes seen in the 

 thin-walled species, and common to most or all of the species 

 of Stenopora, Lonsd., which demands a little consideration here, 

 thoueh its true significance is still somewhat dubious. I allude 

 to the occurrence of peculiar blunt spine-like structures, which 

 are placed, in greater or less numbers, round the calices, usually 

 at the angles of union of the corallites. Various Monticuli- 

 poroid Palaeozoic corals have been noticed by various observers 

 to possess these calicine spines ; and Milne-Edwards and 

 Haime at one time (Brit. Foss. Cor. Intr., p. Ixi) regarded the 

 existence of these structures as dias^nostic of the eenus Steno- 

 pora as defined by them. Structures of this nature are, how- 

 ever, possessed by a large number of true Monliculiporcs, and, 

 notably, hy M. frondosa, D'Orb., J/, hmiida, Phill., M. Jamesi, 

 Nich., M. moniliformis, Nich. (figs. 36, 37), M. gracilis, James, 

 and other forms. As viewed from the surface, these spines 

 present themselves simply as so many blunt projections, which 

 do not seem, so far as I have been able to observe, to be per- 

 forated by any apical apertures. When examined by means of 

 thin sections, however, these spines are found to be in no way 

 of the nature of mere superficial ornaments, but they extend 

 into the substance of the corallum, between the ordinary coral- 

 lites, to a depth equal to that reached by the smaller tubes of 

 the colony. Tangential sections taken a little below the sur- 

 face (fig. 37) show that these apparent spines are composed of 

 concentrically laminated sclerenchyma, exhibiting in their centre 

 a dark circular spot or a clear circular space. There cannot, 



