GLYPHIOCERAS (BEYRICHOCERAS) CORDATUM. 189 



about five-sixths ; umbilicus very deep and step-shaped, with subangular margins 

 and steep sides, the depth from the edge of the outer whorl about 28 mm. ; about 

 one-fourth of the diameter of the shell in width. Whorl distinctly cordate in cross- 

 section in the region of the aperture ; a little wider than high ; indented to nearly 

 one-half of its height by the preceding whorl. Periphery narrowly convex, its 

 boundaries imperfectly defined upon the cast by an obtuse and obscure ridge on 

 each side of it; these ridges are not seen where the shell is present. The periphery 

 becomes acute towards the aperture, when all trace of the ridges disappears. The 

 sides are slightly convex, with a faint obtuse ridge, also upon the cast only, at 

 about three-fifths of the width of the side from the edge of the umbilicus, becoming 

 obsolete, as is the case with the peripheral ridges, on the anterior part of the body- 

 chamber. Umbilical zone well defined, rather narrow, nearly perpendicular to the 

 plane of symmetry of the shell. Body-chamber occupying at least the whole of the 

 last whorl, probably exceeding this limit; aperture not preserved, but the lines of 

 growth upon the test indicate that the peristome was furnished with a prominent 

 lateral crest and a deep and narrow hyponomic sinus. Chambers rather shallow. 

 Suture-line as in PL XL VII, fig. 2 c. Test nearly smooth, with lines of growth 

 which have a nearly radial direction on the inner portion of the lateral area, then 

 bend forwards and finally backwards to form the deep and narrow hyponomic sinus 

 upon the periphery. The cast, especially in the anterior region of the body- 

 chamber, shows distinct traces of the faint lines of growth that ornament the test. 



Di 



mensions. 



Type specimen in Museum of Science and 

 Art, Dublin. 



Diameter of shell .... 11G*5 mm. 



,, umbilicus (edge to edge) . . 28*5 ,, 



,, ,, (suture to suture) . . 26 , ,, 



Height of outer whorl (about) . . . 51'5 ,, 



„ above preceding whorl (about) . . 27*5 ,, 



Thickness at umbilical margin . . . 5G"0 ,, 



The measurements which relate to the diameter of the shell must be taken as 

 approximate, as the shell has been rendered somewhat elliptical by rock pressure. 

 The longer of the two diameters has been given in the dimensions of the umbilicus, 

 the shorter in those of tin 1 shell, as a large piece of the outer whorl has been broken 

 off, making measurements of the longer diameter very dimcull to effect. 



Affinities. — Mr. Crick (loc. cit.) observes that "this species is evidently closely 

 related to such forms as Glyphioceras reticulatum, J. Phillips, sp., 1 and Glyphioceras 

 Davisi, Foord and ( Irick." 



1 'Geol. York.,' pt. ii, 1836, p. 235, pi. six, dgs. 26 32. Also* Cat. Foss. Ceph. British Museum,' 

 pt. iii, 1897, p. L93. - 'Cat. Foss. Ceph. British Museum; pt. iii. L8!>7, p. 198, fig. 95. 



