FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 227 



Genus Glyptodesma. Han. 



Glyptodesma, Hall. N. T. Rep., Vol. 6, pt. 1. 

 Etymology: glyptos, curved; desm-a, a ligament. 



Shell aviculoid, erect or moderately oblique ; inequivalve. Ligament exter- 

 nal. Ligamental area striated, continuous. Hinge with two strong, lateral 

 teeth, and numerous irregular transverse plications along the cardinal margin. 

 In form the shells of this genus resemble Actinodesma, but they have not the 

 permanent diverging teeth of that genus. Surface marked by concentric 

 striae. 



Glyptodesma cancellata. N. SP. 



Plate V., figure 1. 



Shell large, regularly oviform in its body, almost erect or slightly oblique ; 

 height exceeding length ; anterior and posterior margins broadly rounded ; 

 front or base strongly curved ; posterior wing large ; its posterior margin con- 

 cave, and its extremity produced to a salient point ; anterior wing defective 

 in the specimen before me, but it appears to be short, and of the shape as 

 indicated in figure 1, plate 5. The hinge-line is about equal in size to width 

 of the shell. Only the left valve is known ; it is very convex and gibbous in 

 the umbonal region, from where it slopes in a gentle curve to the margins in 

 the basal half of the valve. The lateral slopes of the umbonal region are 

 abrupt, the anterior somewhat more than the posterior. There is no sharp 

 dividing line between the body and wings. The posterior wing is very convex, 

 sloping rapidly or even abruptly to the cardinal line, which is entirely straight. 

 The interior of this shell and its right wing are unknown. The umbo is promi- 

 nent, and the beak elevated and incurved over the hinge- line ; it is located 

 anterior to the middle of the shell, and has an anterior direction. The surface 

 is marked by strong, simple, rounded, radiating plications, with wide, flat 

 interspaces, which are about three times as wide as the ribs. There is scarcely 

 an intercalated plication observed on the whole valve ; no bifurcation takes 

 place. 



The specimen here described and figured is well preserved, with the ex- 

 ception of the anterior wing, which is either broken or covered with rock; this 

 shell measures thirty-one lines in height, by twenty-nine lines in length. The 

 surface is divided by several strong lines of growth into concentric zones. 



Formation and Locality. Found in the Corniferous limestone of the Devonian formation at and 

 around the Falls of the Ohio, in Kentucky and Indiana. The specimen illustrated on plate 5 is, so far, the 

 only one known. 



