Brachiopod Homœomorphy: ‘ Spirifer Glaber ’

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Abstract
It is easy, but it is very dangerous, to group together under one name a series of shells of similar appearance, especially when they are in the smooth catagenetic stage; because this smooth stage may have been attained by the loss of different distinctive features, pointing to polygenetic origins. An instructive case in this respect is found in the series of forms called Spirifer glaber . As Spirifera glabra , Davidson figured a series of shells which do not all agree in being smooth; for, though most of them are smooth, some are radially costate. And they do not agree in shape: some have a pronounced mesial fold, others hardly any; some are very transverse, others are narrow. Then in his synonymy he combined under this name many species of other authors: Sp. obtusus, Sp. oblatus , Sowerby, Sp. linguifera, Sp. symmetrica, Sp. decora , Phillips, Sp. lævigatus , von Buch. Of late years this glaber -series of the Carboniferous, and certain smooth Spiriferids of the Devonian, have been ranged in M'Coy's genus Martinia . A somewhat similar series of Spiriferids is grouped under Reticularia , M'Coy: their distinguishing character is a reticulate surface. Davidson makes the principal species Spirifera lineata (Martin), and ranges under it Terebratula (?) imbricata , Sowerby, Spirifera elliptica and Sp. mesoloba , Phillips, Reticularia reticulata and Martinia stringocephaloides , M'Coy. In Reticularia the ornament is in the catagenetic stage, decreasing in intensity; so that partially or wholly smooth Reticulariœ are to be expected. There is good evidence that several of the forms ranged under Spirifera glabra

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