STROMATOPORA CARTERI. 175 



rately numerous, are all more or less imperfect, none of them showing the base or 

 mode of attachment. The species grows to a large size, and the ccenosteum is of 

 the massive as distinguished from the laminar or discoidal type, the under 

 surface having very possibly been devoid of an epithecal membrane. Latilaminar 

 growth is a very marked feature, and each latilamiua, as is the case in 8. typica, 

 Rosen, consists essentially of a single stratum of radial pillars which extend 

 continuously from its lower to its upper surface, and are united by irregular 

 horizontal or oblique connecting processes, these latter not being sufficiently 

 regular to give rise in vertical sections to the appearance of definite " concentric 

 lamina3." The skeleton-fibre in S. Carteri is of medium thickness, being finer than 

 that of 8. concentrica, Goldf., 8. Hiipschii, Barg., or 8. discoidea, Lonsd., but is 

 remarkable for its coarsely porous structure, as seen in thin sections (Plate I, 

 figs. 6 and 7). A characteristic feature is the peculiarly loose and open nature of 

 the reticulated coenosteal tissue (Plate XXIII, figs. 2 and 3). Another charac- 

 teristic feature is the total or almost total absence of the branched and radiating 

 astrorhizal canals, which are so conspicuous in most species of Stromatopora. In 

 most examples of the present form no traces whatever of these structures can be 

 detected, and in none are these more than the merest indications of their exis- 

 tence. The surface, therefore, is simply smooth or gently undulated, and is 

 entirely without " mamelons." 



I am not acquainted with any undoubted vai'ietal forms of this species, nor 

 have I ever seen a specimen of it in the " Caunopora-state." 



8. Carteri cannot easily be confounded with any other species of the genus 

 Stromatojpora. It agrees with 8. typica, Rosen, and with S. concentrica, Goldf., in 

 its conspicuously latilaminar mode of growth ; but it is distinguished from both 

 these forms by the peculiar character of the skeletal reticulation, as also by the 

 absence of astrorhizas. By this last feature it is equally distinguished from 

 S. Hiipschii, Barg., 8. Beuthii, Barg., and 8. discoidea, Lonsd., while it is further 

 separated from these by the composition of its skeleton out of regular latilaminae. 

 The only species of Stromatopora with which S. Carteri, Nich., is really closely 

 allied is a form from the Silurian Rocks (Upper-Oesel group) of Oesel, which I 

 may provisionally name 8. borealis. The general structure of the skeleton-fibre 

 and of the coenosteal tissue is the same in these two types, a distinct relationship, 

 or, perhaps, an actual identity, being thus indicated. 8. borealis, Nich., is, 

 however, distinguished from 8. Carteri by the fact that the ccenosteum of the 

 former has the shape of a thin extended lamina, with a basal epitheca, while 

 it is not composed of successively superimposed latilarninaa. The astrorhizal 

 system of 8. borealis is, moreover, very well developed. A further point of 

 distinction is found in the fact that the zooidal tubes of 8. borealis are more 

 abundantly furnished with tabulae than is the case in 8. Carteri, while these 



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