30 BRITISH CRETACEOUS BRACHIOPODA. 



and almost flat, carinated and edged ; deltideum occupying less than a third of the width 

 of the area, and diminishing gradually till it reaches the foramen, a very small part of 

 which it encircles ; smaller valve slightly convex, or longitudinally depressed near the 

 front : hinge-line very obtuse and long. Valves ornamented by a great number of small 

 rounded, radiating costse, rarely bifurcating, but augmenting rapidly at variable distances 

 by the intercalation of additional plaits, thus in one specimen eighteen only are seen at the 

 umbo, thirty-three towards the middle, and fifty-six near the margin ; in another at the 

 umbo, fifteen ; near the middle, thirty ; at the edge, forty-four, &c. ; these are likewise 

 intersected at various distances by well-defined concentric lines of growth. Boss or 

 cardinal muscular fulcrum much produced ; loop small, doubly attached ; structure 

 punctuated ; shell very thick, especially at the beak and umbo. Dimensions variable ; 

 length 11, breadth 9, depth 5 lines. 



Obs. This beautiful and elegant species seems to have been first figured and described 

 by Koenig in 1825, under the name of Trigonosemus elegans ; about the same period it 

 was likewise described by Defrance under that of Terebratula elegans and recurva. 

 The typical specimens of both authors having been obtained from the Upper Chalk of the 

 neighbourhood of Valogne. During a late visit to that locality, M. de Gerville kindly 

 gave me many specimens of this shell of all ages, and on the examination of which I felt 

 persuaded that M. Defrance, D'Orbigny, and Bronn are mistaken in proposing to split 

 this type into two species, as we find every insensible gradation between those forms with 

 a depressed smaller valve to those in which it is moderately convex ; this is especially 

 noticeable in younger shells, where the smaller valve is very often nearly flat ; the form of 

 the beak is also variable both in length and curvature. It is but lately that this species 

 has been discovered as occurring in England, and the first knowledge of the fact I owe to 

 Mr. Woodward, who had seen and sketched two specimens found in the Norwich Chalk 

 by Mr. Fitch. Mr. Harris has also procured it from the chalk detritus of Charing, 

 Kent : this species is very rare in England, only three examples having been as 

 yet obtained; all of which will be found illustrated in our Plate IV, figs. 1, 2, 3. These 

 specimens are beautifully preserved, and present those variations which tempted Defrance 

 and others to propose two species. It likewise occurs in the chalk of Ciply in Belgium, 

 also at Freville near Valognes (Dep. de la Manche). 



Plate IV, figs. 1, 1 ah . Specimen, natural size; the largest as yet found from the 



Chalk of Norwich, in the collection of Mr. Fitch. 

 ,, fig. 1 cd . Enlarged illustrations of the same. 



,, figs. 2, 2 B . Another specimen likewise from the Chalk of Norwich, measuring 

 length 9, breadth 8, depth 4 lines ; also from the collection 

 of Mr. Fitch. 

 „ fig. 3. A young specimen from the Chalk detritus of Charing, Kent, 

 measuring length 6, width 6, depth 2^ lines, from the col- 

 lection of Mr. Harris. 





