50 BRITISH CARBONIFEROUS BRACHIOPODA. 



Length 10, width 10|, depth 7 lines. 



}j ^> j> '*2' 3> ^2 >' 



» 52> 5> "> >) 4 J> 



0^*. This spirifer appears to have rarely exceeded the dimensions given above ; and 

 although the number of its ribs is variable, it appears to be in general a well-characterised 

 and easily recognisable species. After an attentive comparison of the original types upon 

 which Professor Phillips had founded his three species, as well as of numerous other 

 specimens of the same in the British Museum, &c.. Professor L. de Koninck and myself 

 have arrived at the conclusion that Sp. frisulcosa, figs. 7, 10, 11, and 12, Sj). 

 triradialis, figs. 8 and 9, and 8p. sexradialis, figs. 4, 5, and 6, are only different states, 

 conditions, or varieties of a single species. It has appeared to us evident that in Sp. 

 irisulcosa and in Sp. triradialis the smooth or unoccupied space on either valve is 

 occasioned by the last ribs, having been either obliterated or not produced by the 

 animal, for in many individuals they are clearly indicated, although not completely 

 developed. 



In a few exceptional specimens, as many as eight ribs have been distinctly counted 

 on either valve, while in a few still more rare instances, such as in the type specimen of 

 Sp. trisulcosa, fig. 12, none of the lateral ribs are clearly defined. It would, therefore, 

 appear desirable as well as rational to retain but a single name for the different conditions 

 presented by this variable shell, for otherwise we would be obliged to make as many as 

 four species, based upon the number of ribs each specimen might possess. I have, there- 

 fore, retained the term Sp. triradialis in preference to the other denominations, simply 

 because it represents the intermediate and most common condition in which the species 

 is fovmd ; but, as a general rule, it is always objectionable to give names to species derived 

 from the number of ribs some individual example may possess. 



Loc. The different varieties of this species have been found by Professor Phillips, 

 the late Mr. Gilbertson, and others, in the carboniferous limestone of Bolland. It has 

 also been found in Derbyshire. I am not acquainted with any Lish specimen, but it 

 has been obtained from the Carboniferous shales of Lanarkshire in Scotland. It is a rare 

 fossil at Vise, in Belgium, where it has been discovered by Professor de Koninck. 



Spirifera PiNGUis, Sowcrhy. Plate X, figs. 1 — 12. 



Spirifeka PINGUIS, Sow. Miii. Cou., vol. iii, p. 125, tab. 2/1, 1820. 



— ROTUNDATA, J. de C. Sow. Mill. Coll., vol. v, p. 89, tab. 461, fig. 1, 1824 (not 

 , , Anomites rotundatus of Martin). 



— — Sow. Davrcux, Coast. Geogn. de la Province de Liege, p. 272, 



pi. 7, fig. 8, A, 15, 1831. 



— — Sow. Phillips, Geol. of Yorkshire, vol. ii, p. 218, pi. ix, fig. 17, 



1836. 



