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s^.oping on each side of the beaks. Both valves are gently and uniformly 

 convex. The ventral valve has often a barely perceptible mesial sinus ; 

 the umbo small; the beak not incurved; the area very narrow, scarcely 

 exceeding the thickness of the shell ; the foramen (as seen in detached 

 fragments) triangular and open to the beak ; the small chamber at the beak 

 almost exactly Hke that of S. Icevis, and S. microcamerus, as figured by 

 Sowerby, M'Coy, and Davidson. The dorsal valve sometimes gives 

 indications of an obscure mesial fold ; but, in general, it is uniformly 

 convex. I have not seen the area of this valve, but it must be linear ; 

 there is no umbo. Surface with several concentric imbrications of growth, 

 and with very narrow obscure ribs, three or four in two lines, curving out- 

 wards to the sides, and some of them upwards to the hinge-line. These 

 are also crossed by fine concentric wrinkles. When the specimens are 

 slightly exfoliated all the surface-characters disappear. 



" Length of the largest specimen seen, twenty-five lines ; greatest 

 width of the same, at about the mid-length, thirty-three lines. Some of 

 the specimens indicate a greater proportional length. 



" There is no other known species with which this need be compared 

 except S. Icevis, Sowerby, as described by M'Coy, under the name of 

 Pentamerus niicrocamerus (Brit. Pal. Foss., p. 210). The width of 

 that species, in proportion to the length, is stated to be as fifty-five is to 

 one hundred, whereas in this it is, on an average, about eighty to one 

 hundred. This great difference in proportions rarely occurs in the same 

 species. Messrs. Davidson and Salter are of opinion that M' Coy's 

 P. microcaments is identical with S. lens- Be that as it may, the figure 

 of S. Icevis, given by Sowerby in ' Sil. Syst.,' pi. xxi., fig. 12, seems to 

 be distinct from S. lens, and also from^\ Salterii. He says (^Op. cit., p. 

 638), ' Semicircular, compressed, smooth; a slight elevation along the 

 middle ; beaks rather prominent, the area between them narrow, with 

 parallel edges. Length, ' eight lines ; width, twice as much.' The 

 words ' elevation along the middle " could only apply to the dorsal 

 valves of S- lens and S- loevis, in neither of which can the dorsal foramen 

 be seen, when viewed in the position in which Sowerby's specimen is 

 drawn, as it is in the figure cited- This figure, however, always appears 

 to me to exhibit a sinus rather than a fold, in which case it would be a 

 ventral valve. Judging from Mr. Davidson's figures, I should say that 

 the upper part of the ventral valve of S. lens must be of a very different 

 jorm from that of the specimen represented by Sowerby. 



This species is dedicated to the late J. W. Salter, Esq., F.G.S., 

 Paleontologist to the Geological Survey of Great Britain. 



Locality and Formation. — Strkldanclinia Salterii occurs at Heath 



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