14 CANADIAN FOSSILS. 



H. PLAXULATA, N. Sp. 



Plate II. Figure 5-7, and Variety, figure S. 



H. unciam lata, anjractibus 4 grailatis, concent rice sulcatis, supra plants; 



carina ad angulum externum elcvatd ; basi tumido late umbilicato. 



Synonym. — [Euomphalus uniangulatus, Hall, Palaeontology of New 

 York, vol. L, plate 3, figure 1 '?] Scalites uniangulatus, Salter, in 

 British Association Reports for 1S51, Trans. Sect., p. G3. 



Prof. Hall's specimens of the very nearly allied Euomphalus unian- 

 gulatus are so depressed, that " the spire scarcely rises so high as the 

 angular ridge on the upper and outer edge of the last whorl." Ours 

 are generally more elevated. His specimen too shews the umbilicus 

 entirely open, and the shell therefore truly discoidal, while in ours 

 at least half the whorl on the lower side is covered by the preceding 

 one. They are probably therefore distinct species. 



The general form is depressed, the whorls being nearly flat above, 

 and rising a little above each other in a step-like manner, each whorl 

 nearly twice the breadth of the preceding. They are bluntly carinate 

 on their outer upper angle, and the carina is elevated (but is not a 

 true band), the distinct lines of growth being curved backwards to 

 it, and beneath it bent abruptly forwards. The whorl is concave 

 for a short space beneath the keel, and then tumid over the sides 

 and base. Concentric furrows occur on the margin to the number 

 of four or five, and are often duplicate, three of the intervening 

 ridges being more conspicuous than the rest. 



The base is smooth, except the prominent lines of growth ; the 

 umbilicus steep, nearly half of each whorl exposed in it, and its 

 edge is not angular, except in the young whorls. 



The mouth is rounded, about as high as wide, and has the upper 

 margin retreating towards the deep notch, and the lower edge 

 brought forward. No reflection of the inner lip takes place in this 

 species, and the general aspect is that of Euomphalus. 



Variety Muricata. Figure S. 



Instead of the plain ridges round the outer border of the whorl, 

 there are three spinose or tuberculate ridges (like those of H. spifiosa, 

 figs. 9, 10), but the tubercles are not strictly regular in position on 

 the ridges, though they occur all round the shell. They may be 

 extraneous, and so may those of the following species. 



