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BRITISH CARBONIFEROUS BRACHIOPODA. 



Phillips judiciously united into one species T. acuminata and platyloba, as well as the 

 above-named varieties, but was perhaps mistaken while forming a new and separate species, 

 T. mesogonia, for what seems to be a small variety of the typical shape of Martin's shell, 

 and which the distinguished author of the ' Geology of Yorkshire' himself states to be 

 " a miniature copy of the first var. of T. acuminata." Such would appear to be the named 

 varieties and synonyms of the species under description, but it is necessary here also to 

 record that several Palaeontologists, and especially Professor M'Coy, would go still further, 

 by adding Bh. pugnus, of Martin, to the varieties of B. acuminata ; and although I am 

 ready to admit that some extreme and exceptional shapes of both may be difficult to deter- 

 mine, and might lead to the idea of a passage, still the generality of specimens of both 

 species appear to me so distinct that I would not feel myself justified in subscribing to the 

 opinion advocated by the distinguished Irish professor. 



In his great work on 'Belgian Carboniferous Fossils,' published in 1843, Professor de 

 Koninck had assembled, as synonyms of Bh. acuminata, several species which he subse- 

 quently admitted to be distinct, at p. 664 of the supplement to that work, published in 

 1851, and among other observations he states it to be his decided opinion that B. pugnus 

 is specifically distinct from B. acuminata. 



Long and careful observations, based upon the study of many specimens, has induced 

 some palaeontologists as well as myself to consider that, although the typical form of the 

 species under description may be heart-shaped, smooth, with a long, sharpened, pointed, 

 cuneiform sinus (as described by Martin and others), the greater number of specimens did 

 not present that character, the sinus being more uniformly rounded in front, and regularly 

 or irregularly marked with rudimentary or prominent ribs, and of these Sowerby has 

 formed his varieties sulcata, plicata, and platgloba. In PI. XXI, fig. 10, a specimen is 

 represented in which the ribs extend from the frontal margin to nearly the extremity of 

 the umbone, and if the reader will again look at PI. XXI, he will find that in figs. 

 1, 2, and 3, the fold, or what corresponds to it, is smooth and acute, while in fig. 4 it is 

 divided into two, in fig. 5 into three ; fig. 6 shows five ribs, and so on until the fold and 

 sinus become regularly and numerously plaited, as in figs. 7, 10, and 11. The great 

 elevation of the front is also at times gradually replaced by a more gentle curve, and in 

 the young state especially the whole shell very often appears to be but slightly convex, and 

 is even depressed, as in figs. 14 — 20 of the same plate. In the generality of specimens 

 we find not a vestige of a rib on the lateral portions of the valves, but in other rarer 

 examples these are sometimes present near the margin, and it is specimens so constructed 

 that approach most in shape to Bh. pugnus. All this extreme variability, offered by a 

 single species, shows how cautious we should be in our appreciations of specific 

 characters, and especially so when we are unavoidably deprived of all anatomical 

 assistance. 



Mr. Hancock has stated in his admirable ' Memoir on the Anatomy of the Brachiopoda,' 

 published in the 'Philosophical Transactions of the Royal Society ' for IS 58, that two 



