228 PALEONTOLOGY OF KENTUCKY. 



Glyptodesma occidentale. HALL. 



Plate III., figure 5. 

 Glyptodesma occidentale, Hall. Pal. N. Y., Vol. 5, part 1, page 1571884. 



Shell large, broadly ovate ; body nearly erect ; height somewhat greater than 

 the length. The specimen before me measures thirty-eight lines in height by 

 thirty-four lines in length. All the margins are regularly curved, with about 

 the same radius. 



Of the two valves of the shell, only the left one is known ; it is somewhat 

 gibbous at the umbo, from where it slopes in a gentle curve down to the base 

 and to the basal half of the anterior and posterior margins ; in the upper half 

 of the valve the lateral slopes of the umbonal region are abrupt, more so on 

 the anterior than on the posterior side. The hinge-line is straight and con- 

 siderably shorter than the width of the shell ; in our specimen it measures 

 about two- thirds of the greatest width of shell. Prof. Hall's figure, on plate 

 86, of volume 5, part 1, shows an enormously extended wing, and consequently 

 a very large hinge-line, but it appears to me, that in restoring the wing, which 

 in Prof. Hall's specimen was missing to the extent of an inch and one-quarte 

 on the posterior margin, a considerable mistake was made in regard to its 

 length, although the concentric lines, near the edge of the broken wing, indi- 

 cated a very mucronate one. My specimen is almost perfect and shows a wing 

 as illustrated in figure 5, plate 3. The beak is anterior to the middle of the 

 shell, with a strong inclination to the anterior end ; it is prominent and acute. 

 The anterior wing is short, defined by a deep sulcus, and marked byssal in- 

 flection or sinus just anterior to the beak. Posterior wing is large, depressed, 

 convex, moderately extended, joining the body of the shell at the middle, and 

 defined partly by the recurving of the striae, but more decidedly by a small 

 but plainly visible depression, which extends in a straight line from the cardi- 

 nal line near the beak along body of the valve to the posterior margin at the 

 middle of the shell. The posterior margin of the wing is slightly concave, 

 and its extremity somewhat produced, but not to such an extent as shown in 

 Prof. Hall's figure. 



Test thick, marked by numerous fine striae or lines of growth, which at inter- 

 vals are crowded into fascicles, producing an undulating surface. These striae 

 are more closely arranged, and become lamellose on the anterior part of shell. 

 On the posterior wing the striae are regular, and at distant intervals a single 

 stria becomes sharply elevated. The interior of this shell and its right valve 

 are unknown. 



This species resembles G-. erectum, but appears to be a more robust form ; 

 the shell is more orbicular, the umbonal region more gibbous, the surface more 

 rugose from the undulations of the fascicles of striae, and the limitation be- 



