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II.—On Heterastræa, a new Genus of Madreporia from the Lower Lias

Published online by Cambridge University Press:  01 May 2009

Robert F. Tomes Esq
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Extract

During the interval of ten years which has elapsed since my paper on Liassic Madreporaria was read at one of the meetings of the Geological Society, a great many specimens of Liassic Isastrææ and Septastrææ, chiefly from the Vale of Evesham, have come into my hands, and with this abundance of material I have examined a new the several species, and have arrived at the results contained in the present communication. When making these examinations, I have been invariably struck with the absence of a distinct and well defined basal wall and epitheca. Further observation also showed that these Liassic forms differed from other Isastrææ in having occasional elongated calices, like those of Latimæandra.

Type
Original Articles
Information
Geological Magazine , Volume 5 , Issue 5 , May 1888 , pp. 207 - 218
Copyright
Copyright © Cambridge University Press 1888

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References

page 207 note 1 More than seventy specimens have been examined and contributed to the results made known in this paper.

page 207 note 2 It has become necessary that gemmation in the genus Isastræa should receive further attention. It has been variously stated both by Prof. Duncan and by me to take place within the calice, as well as on the margin of the wall which surrounds it. Thus in the descriptions of Isaslræa endothecata and I. latimæandroidea, Prof. Duncan says it is marginal (“on the margin” are the words made use of in the description of the latter species). More recently, however, he has asserted that “the gemmation of Isastræa certainly does not take place between the walls of corallites, but within the calicular margin; it is between the margin and the centre of the calice.” I am not aware that it has ever been spoken of as occurring between the walls, though I, as well as Prof. Duncan himself, have spoken of it as occurring both inside the calice and on the margin of the wall. Edwards, MM.Milne and Haime, (Hist. Nat. Coral, vol. ii. p. 626)Google Scholar speak of it in these words, “ Les polypierites se multiplient par gemmation calicinale et submarginale,” while M. de Fromentel says it is “submarginale.” The present communication by removing the Liassic species from the genus Isastræa altogether, will materially lessen the difficulty of future classification.

page 209 note 1 MM. Milne Edwards and Haime define the budding in Heliastræa in the following words: “Les nouveaux individus produits par bourgeonnemeut se montrent dans les diflierents espaces intercalicinaux.” Probably gemmation in Elysastræa also took place in the intercalicular spaces.

page 211 note 1 It is necessary to notice here a variation in the process of splitting that takes place in different calices, or even in the same calice. The two opposite and approaching septa do not always meet and make the division until a new calice has been actually formed, and it is common for two or three fossulfe to make their appearance in a long calice with only some, or even without any, dividing septa. When this is the case, there is some resemblance to Latimæandra. However, the septa always become elongated sooner or later, and fissiparity is then complete. M. de Fromentel gives a good account of the process in his description of the so-called Septastræa excacata.