On the structure and affinities of the genus Monticulipora and its sub-genera, with critical descriptions of illustrative species . onclusion, though I donot feel disposed to assert positively that , DOrb.,with its various abnormal characters, is an indisputable Mon-ticuliporoid. In Heterodictya, Nich., we have to deal with anundoubted Polyzoon, of the general type of Ptilodictya. Thecolony forms a thin falciform expansion which is composedof two layers of tubes diverging in opposite directions froma definite striated median calcareous lamella, and which isbounded by perfectly definit
On the structure and affinities of the genus Monticulipora and its sub-genera, with critical descriptions of illustrative species . onclusion, though I donot feel disposed to assert positively that , DOrb.,with its various abnormal characters, is an indisputable Mon-ticuliporoid. In Heterodictya, Nich., we have to deal with anundoubted Polyzoon, of the general type of Ptilodictya. Thecolony forms a thin falciform expansion which is composedof two layers of tubes diverging in opposite directions froma definite striated median calcareous lamella, and which isbounded by perfectly definite margins, and has a perfectlydefinite shape. As regards internal structure, the only re-semblance between Heterodictya and any of the Monticuli-poroids is to be found in the existence in the former of well-developed tabulae (fig. 15, a and b), which, however, are oftenincomplete. No interstitial tubes are present, nor are thereany monticules or structures comparable with these. RELATIONS TO EXTINCT ORGANISMS. 89 I do not myself know of any Monticuliporoid which couldbe compared with Heterodictya except M. pavonia, DOrb.: and. Fig. 15.—Minute structure o^ Hdcrodictya gigantea, Nich., from the Corniferous Lime-stone (Devonian) of Canada. A, Vertical and longitudinal section, showing the well-developed tabulre; B, Vertical and transverse section, showing the incomplete conditionof many of the tabulre; c, Tangential section. All tlie figures are enlarged eighteentimes. this is, in my opinion, sufficiently separated from the former byits want of any definite form, or of definite and structurallydifferentiated margins ; by the absence of a complete mediancalcareous lamina, which is so clearly a distinct structure thatthe layers of tubes can be readily stripped away from it; andby the possession of distinct * monticules. The tabulae ofM. pavonia, DOrb., are even more feebly developed than inHeterodictya; but this is a feature of no importance—whereasthe striking difference in gen
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Keywords: ., bookauthornicholso, bookcentury1800, bookdecade1880, bookyear1881
