146 BRITISH CARBONIFEROUS BRACHIOPODA. 



lations, and from which at intervals project short slender spines. Dorsal valve very con- 

 cave, following the curves of the opposite valve, and similarly sculptured. In the interior of 

 the ventral valve, the muscular impressions are located in the rostral portion of shell close 

 to the extremity of the beak. 



Dimensions variable : a large example measured, length 2 inches, width 4^ inches ; a 

 small one, 2 lines by 4. 



Obx. At p. 463 of his ' British Palaeozoic Fossils/ Prof. M'Coy mentions that " the 

 magnificent suite of specimens of P. giganteus now in the University Collection enables him 

 to state positively that the distinctions relied on by M. de Verneuil in the ' Geology of 

 Russia/ and M. de Koninck in his ' Monograph of Productm' for separating P. htfis- 

 simvs from P. giganteus, do not really exist ; several specimens in the collection showing 

 in one individual the gradual conoidal passage of the ear into the body of the shell (as in 

 P. latissimus), on the one side, and a narrow sub-cylindrical ear, projecting abruptly from 

 the side of the defined gibbous body of the shell (as in the P. giganteus), on the other: 

 that the other characters mentioned as distinctive by them and the older authors, such as 

 thinness of the shell, and few or no longitudinal folds, greater depression of the ears, &c, 

 are characters of the young shell, and particularly the entering valve : further, both forms 

 (contrary to what those authors suppose) occur together in abundance in the same bed in 

 Northumberland." This is not, however, the opinion of the larger number of palaeon- 

 tologists, who cannot recognise in the peculiar spindle shape of P. latissimus a simple 

 variation in form of P. giganteus; and I must confess that the examinations I have made of 

 many examples of both would not enable me to arrive at so positive an opinion as that of 

 the distinguished author above quoted, although I would not dispute the possibility of 

 its being correct. At all ages and dimensions, from that of four lines in breadth to four 

 inches and a half, the shell appears to retain its very transverse appearance ; and its 

 interior dispositions, although similar in character to those of giganteus, appear to 

 me somewhat different in their minor details, and, notwithstanding what has been asserted 

 by M'Coy, the shell seems to me much thinner than that of Martin's species. 



In England, P. latissimus is common in the limestone and shales of various localities. 

 Sowerby mentions that it occurs in a cherty limestone at Tyddmaur Farm, in Anglesea; it 

 is not uncommon at Settle in Yorkshire, Fountains Fell, Kirby Lonsdale, in Northum- 

 berland, &c. In Scotland, it is one of the most characteristic species in some of the lower 

 stages of the Carboniferous system : it is found in Lanarkshire at two different levels ; thus 

 at Belston Burn it occurs at 265 fathoms below "Ell Coal," and 391 at Braidwood 

 Gill, also at Brockley, near Lesmahago ; in Renfrewshire, at Arden Quarry, Thorn- 

 liebank ; in Ayrshire, at Roughwood and West Broadstone Beith, &c. ; in Stirlingshire, 

 in the Craigenglen (Campsie) beds. In Ireland, it is stated by Mr. Kelly to occur 

 in the calciferous slate and carboniferous limestone of Lisnapaste, Killymeal, and 

 Raheendoran. On the Continent, it has been found at Vise in Belgium, and in several 

 Russian localities. 



