﻿QUADRATE. 



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Ibbetson and Forbes, Proc. Geol. Soc, vol. iv, p. 414, 1844. 

 Fitton, Quart. Journ. Geol. Soc, vol. iii, p. 317, 1847. 



D'Orbigny, Paleontologie Franchise, Terr. Cret., vol. iii, p. 145, p 1 . 292, 1843. 

 Ib., Prodrome de Paleont, vol. ii, p. 161, No. 322, 1850. 



Pictet and Renevier, Foss. du Terr. Aptien de la Perte du Rhone et des Environs de 

 Ste. Croix, pi. xii, fig. 1, 1857. 



The figure of T. dadalea is ovately quadrate and depressed; the apices are small, 

 pointed, slightly recurved, anteal and terminal ; the hinge-border is short and slightly 

 rounded, forming nearly right angles with the anterior and posterior borders ; the 

 latter or siphonal border is equal in length to the hinge-border, its lower extremity is 

 curved ; the lower border is curved elliptically with the anterior border. The area 

 constitutes half the surface of the valve • it is flattened, without any distinct mesial 

 division, excepting near to the umbo; its separation from the costated portion of the 

 surface forms an angle which is slightly ridge-like where it is crossed by the first-formed 

 or apical costellse ; there is, therefore, no distinct marginal carina ; the positions of the 

 inner and median carinae are each indicated by an ill-defined row of small, rounded, 

 widely separated tubercles ; there are also numerous, small, irregular depressed tubercles 

 scattered confusedly over its surface, and also some transverse rugose plications posteally. 

 The upper or apical portion of the area has about eight rows of narrow, ridge-like, 

 delicately knotted costellae, which, originating at the anteal portion of the superior 

 border, and passing across the valve obliquely downwards, enlarge rapidly and become 

 rounded after they have passed the divisional angle, forming tuberculated varices about the 

 middle of the costated portion of the valve, where they are bent suddenly upwards to 

 the anteal border, each forming nearly a right angle ; these are succeeded by several 

 short supplementary varices, which pass backwards horizontally from the anterior 

 border until they are interrupted by the short bent varices. The remaining portion of 

 the surface is occupied by about eight larger, curved rows of tuberculated varices, each 

 row having about nine distinct rounded tubercles ; the rows commence at the angle of 

 the valve and enlarge rapidly downwards towards the pallial border, the smallest 

 tubercle in each row is, therefore, at the angle of the valve or at the usual position of the 

 marginal carina. The escutcheon is narrow, lengthened, and flattened ; it has several 

 obscure rugose varices. The fragment figured by Parkinson, which has priority as an 

 example of this species, appears to represent a specimen with the apical portion of the 

 ornamentation unusually small and more than usually irregular anteally. This arrange- 

 ment differs somewhat from the fine adult specimen figured in the ' Mineral Conchology,' 

 but approximates to some of the Blackdown examples (see Plate XXII, fig. 7). The few 

 first-formed rows of varices form, in some specimens, angulated ridges, which are only 

 slightly tuberculated, resembling the little T. quadrata, Sow., but commonly, as in the 

 figure of Parkinson, the first-formed rows are distinctly tuberculated. The interiors of 



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