KINGENA. 43 



short, much recurved, and truncated by a middle sized foramen, generally lying close on 

 the umbo, so that little or none of the deltidium is seen ; but when exposed, especially in 

 young shells, it is composed of two plates, generally lateral and disunited ; a small portion 

 of the circumference being completed by the umbo ; beak ridges well defined, exhibiting a 

 flat or concave false area between them and the hinge margin ; smaller valve less convex 

 than the dental one, no mesial fold or sinus perceptible, but the margin line in front pre- 

 sents at times a slightly elevated curve. Structure punctuated and irregularly covered by 

 a multitude of small granulations or short hollowed spines, often very large in comparison 

 with the dimensions of the shell, and closely or more widely separated. The largest British 

 specimen yet found, measures, length 12, width 12, depth 7 lines; others, length 9, 

 width 6, depth 5 lines, &c. 



Obs. This interesting shell has given me great trouble from the variability of its shape, 

 and it was not before having minutely examined with much care a vast number of 

 specimens, that I came to the conclusion, that this species existed in the Upper Green 

 Sand, Gault, Lower and Upper Chalk ; its stratigraphical and vertical range is therefore 

 very great. Secondly, that Ter.pentangulata of Woodward, Ter. Hebertiana of D'Orbigny, 

 Ter. sexradiata of Sowerby, Ter. spimdosa of Morris, are all variations of one and the 

 same type, viz., Ter. lima of Defrance. The interior of all are exactly similar ; the structure 

 the same, as well as all the other characters, though these may be slightly modified in 

 appearance in some beds and localities, owing to the matrix and other local causes ; for 

 example, if we take a small or young specimen of Ter. lima of Defrance, and compare it 

 with a large specimen of Ter. pentangulata of Woodward, we perceive an apparent 

 difference, but this is also seen in all extremes of any variable form ; but if, however, we 

 have a great number of specimens of the same species they will soon fill up all the links 

 separating the two extremes by insensible passages, and this is just what I have found in 

 T. lima, from the study of more than a hundred specimens obtained from the different 

 deposits above alluded to ; in the young, the shell is often somewhat compressed, but in 

 all adult individuals it is more or less convex. To afford facility of comparison, I have given 

 in Plates IV and V no fewer than forty-four figures from specimens found in all the beds 

 mentioned, and from different localities ; which I have carefully compared with the types 

 found in the Green Sand of Havre, whence Defrance's original types were obtained. 

 M. D'Orbigny does not appear to have noticed the fact, that on well-preserved shells of 

 his so-called Ter. Hebertiana, the same granular spinose asperities noticed in Ter. lima 

 do exist ; all his specimens were worn on their surface, and only the punctuations visible, 

 which he states to be strongly marked with checkcrwise spaces between. Mr. Woodward 

 first called my attention to the granulation in some from the Chalk of Norwich, and since 

 then, I owe to the kindness of Mr. Fitch, a beautiful series, showing that it was as entirely 

 and as closely covered, as any specimen from the Upper Green Sand. Let any observer 

 compare for illustration, PI. IV, figs. 21 and 22, from the Upper Green Sand, with figs. 19 

 and 20, the types of Ter. pentangulata, from the Norwich Chalk, and they will be at a loss 



