SANGUIiNOLITES PLICATUS. 389 



the valve, becoming more marked and wider apart; as tbey reach the oblique fold 

 they are curved upwards obtusely, whence they pass upwards and forwards to 

 terminate in the hinge-line. Shell very thin. 



Dimensions. — PI. XLV, fig. 4, from the Limestone of Lowick, measures — 

 Antero-posteriorly .... 145 mm. 

 Dorso-veutrally . . . .37 mm. 



From side to side . . . .12 mm. 



Localities. — England : the Carboniferous Limestone of Lowick, and the 

 Redesdale Ironstone, Northumberland. Scotland : Brunston Colliery, Penicuick, 

 ten fathoms below the Linn Spout Limestone, Grarpel Water, and Orchard. 

 Ireland: Roughan, Dungaonon ; Benburb, Tyrone; Ballynascreen and Desert- 

 martin, CO. Derry ; Balliutrillick ; Fermanagh, in calcareous grit and shale ; 

 Riddlestown, Limerick. 



Observations. — Portlock unfortunately figured as the tj'^pe of his Sanguinolaria 

 ^dicata a very young shell, so that it is not surprising that M'Coy described tlio 

 adult form under a different name. The latter author figured the shell twice, 

 and gave a very full and accurate description in his later work, but he does not 

 appear to have observed any but full-grown specimens, for nothing is said about 

 the earlier stages of growth. Probably another reason why the identity of 

 S. plicatus and 8. iridinoides was not recognised is that the large full-grown 

 shells are largely or entirely destitute of shell, and exist as casts of the interior. 

 A fine series of shells is in the Woodwardian Museum, Cambridge, from Lowick, 

 demonstrating the stages of growth and the identity of Portlock's and M'Coy's 

 species. The type of 8. plicatns is preserved in the Museum of the Geological 

 Survey, Jermyn Street, and I am kindly permitted to refigure it by the 

 authorities (PI. XLIV, fig. 11). It consists of both valves, with the test 

 preserved, lying flat open in a shaly matrix. PI. XLIV, figs. 13 and 14, are from 

 Lowick, and represent various stages in the growth of the shell. 



I am unable to agree with M'Coy's statement that 8. 'plicatus was "slightly 

 gaping at both ends," for the reverse is really the case; although, owing to 

 fossilisation often taking place when the valves were somewhat apart, a false 

 appearance of gaping ends is sometimes shown. With the following remark of 

 M'Coy I so cordially agree that I quote it entire : — " The thick internal ridge 

 below the cardinal margin, which leaves a strong sulcus in the cast, is thickest at 

 the posterior end, and gradually tapers to a point and disappears before reaching 

 the beak, so that it is in no way homologous with the cartilage-ridge of 

 Edmondia." This sulcus is well seen in PI. XLV, fig. 4. There is no 

 evidence of any external ligament in this species, in which character it agrees 

 with most of the species of the genus ; and it is possible that this ridge may have 

 served for the attachment of a strong internal ligament, which would be very 



