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SUPPLEMENT TO THE BRITISH 



Genus Thecidium, Def ranee. 

 47. Thecidium ornatum, Moore. Sup., PI. XIII, figs. 5 — 9. 



Thecldeum ornatum, Moore. The Geologist, vol. iv, p. 96, pi. ii, figs. 1 — 3, 1861. 



Shell small, rather longer than wide, pyriform ovate, rather broad, rounded, and 

 slightly indented anteriorly ; hinge-line straight, shorter than the width of shell. Dorsal 

 valve semicircular, slightly convex, depressed towards the front, most convex at the 

 umbo. Surface smooth, marked by concentric lines of growth. Hinge-line narrow. 

 Ventral valve much thickened, and deeper than the opposite one ; beak large, produced, 

 and slightly incurved, callous, and attached by a considerable portion of its truncated 

 posterior extremity. Area triangular, deltidium scarcely defined and much flattened. 

 In the interior of the ventral valve there exists a longitudinal ridge, which divides the 

 interior into two parts. To this median ridge two slender septa, originating under the 

 dental processes converge to become united to the central septum at about half its length, 

 and thus forming two oval depressions. A granulated ridge encircles the shell at a short 

 distance from the margin. In the interior of the dorsal valve there exists between the 

 sockets an oblong or squarish, concave, prominent cardinal process. A short granulated 

 margin to a great extent encircles the valve and forms a bridge over the small, deep, 

 visceral cavity. The granulated ridge, when it reaches the front, becomes inflected 

 upwards in a /^-shaped form, and two branches terminate or unite posteriorly in a point 

 at a short distance from the bridge. From the angular termination of the above- 

 described riclge are thrown off two delicate, curved lamella?, and from which project on 

 each side two spur-like processes. 



Obs. Mr. Moore observed in his description of this species that " the preservation of 

 the loops as shown in the enlarged figure is remarkable, since in the original specimens it 

 is in substance scarcely thicker than the finest unspun silk, and extremely brittle. The 

 interiors of the Brachiopoda are only to be developed by careful manipulation in 

 dissecting or opening up the valves. Many of the interiors of the Thecididge are very 

 beautiful ; but I have never as yet seen any species equalling in delicacy of structure that 

 under consideration." 



I have seen some ten or eleven specimens of this species obtained by Mr. Moore 

 from the Coral Rag of Lyneham, Wilts, where the shell is said to be not uncommon. 

 It does not appear to have much exceeded one line in length and breadth, but varies a 

 good deal in shape, some specimens being more transverse or elongated. There exists 

 also a good deal of variation in the degree of deviation in the central granulated ridge in 



