{mperfectly-hnown Species of Stromatoporoids. 15 



irregularly developed, the vesicles being sometimes of mode- 

 rate dimensions, but being at other places of large size and 

 irregular form. The vesicles have their convexities turned 

 upwards, and the radial pillars terminate upwards in pointed 

 extremities. 



Obs. All the examples of this species which I have exa- 

 mined are in a highly mineralized condition, and are not in a 

 state to allow of the satisfactory working out of minute struc- 

 tural details. That the specimens are rightly referable to the 

 genus Lahecliia is, however, clear, and there can also be no 

 doubt as to the distinctness of the species. Many of the 

 specimens which I have collected, both from America and 

 Kussia, have the skeleton replaced by calcite ; but I have here 

 figured a vertical section of a Russian example in which the 

 skeleton is preserved in the normal manner. The species is 

 most nearly allied to L. conferta^ Lonsd., but is sufficiently 

 distinguished from it by the much more irregular development 

 of the radial pillars and the correspondingly irregular develop- 

 ment, as regards both size and shape, of the interstitial 

 vesicles. 



Formation and Locality. Ordovician formation (Trenton 

 Limestone), Peterborough, Ontario. Also in the same forma- 

 tion (Upper " Jewesche Schichten " or " Wassalem beds"), 

 Saak, Esthonia. [It is interesting to notice that another 

 Trenton fossil, viz. Solenopora compactay Bill., sp., is also 

 common at Saak.] 



Lahecliia serotina, Nich. (PI. II. figs. 3 and 4.) 



Labechia serotina, Nicholson, Mon. Rrit. Stromatoporoids, p. 45, wood- 

 cut, fig. 4 (1885) (figured but not described). 



General form and surface of the coenosteum unknown. 

 In internal structure the skeleton is composed of cylindrical 

 radial pillars, which have a diameter of about ^ millim., and 

 which are traversed by large axial canals. The canals of the 

 pillars are provided with curved internal partitions, which run 

 transversely to the canal, and have their convexities turned 

 upwards. The pillars are very rarely isolated, but are mostly 

 in contact laterally in such a way that they give rise to sinu- 

 ous rows, forming a network of much the same pattern as that 

 produced by the corallites of Halysites escharoides^ Linn. The 

 interspaces between the winding rows of pillars are crossed by 

 delicate calcareous fibres or plates, which connect the pillars 

 together, and which are only rarely and partially vesicular. 

 These connecting plates are usually straight, and are only 

 occasionally curved; hence they give to vertical sections the 

 aspect of a tabulate coral. 



