EARLY DEVOXIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA I 69 



duplicate. Before duplication begins there are 25 of these plications and 

 at the front margin about double that number. The muscular scar of this 

 valve is particularly small. Rhynchonella ramsayi is a shell of 

 these proportions and degree of plication with a similarly obscure median 

 sinus ; apparently the plications are, however, simple instead of duplicate. 

 It is one of the rare forms from the Oriskany of Cumberland, Md. 

 Locality. The single specimen is from Grande Greve. 



Camarotoechia excellens (Billings) 



Plate 28, figure 18 



Rhynchonella excellens Billings. Palaeozoic Fossils. 1874. v. 2, pt i, 

 p. 36, fig. 17, 18 



Original description. Subcircular or obscurely subpentagonal; slope on each side of 

 the beak concave; sides broadly and uniformly rounded; front margin, with about one 

 third the width of the middle, either straight or gently concave. Greatest width about the 

 mid-length or a little in front thereof; width about one sixth or one fifth greater than the 

 length. Ventral valve moderately convex; most elevated at about one third the length 

 from the beak; mesial sinus, at the front margin, about one third the whole width of the 

 sliell; flat in the middle or uniformly concave, deeply indenting the edge of the dorsal 

 valve [fig. 18], but becoming nearly obsolete at about one fourth the length from the margin, 

 and disappearing entirely at about half the length of the valve. Umbo small; beak closely 

 incurved down to the umbo of the dorsal valve. Dorsal valve somewhat more strongly con- 

 vex than the ventral; the outline on aside view nearly parallel with the plane of the lateral 

 margin for about two thirds the length from the front, then abruptly curved down to the 

 beak. Owing to the depth of the sinus the front margin, on a side view, is nearly squarely 

 truncated for about half the depth of both valves. The mesial elevation is either uni- 

 formly convex or a little flattened in the middle, usually gently sloping but sometimes 

 abruptly elevated at the sides of the margin. It becomes obsolete at one half the length 

 of the shell. 



Surface with thirty to forty rounded or subangular ribs (counted at the margin). 

 Some of these on the mesial fold of the dorsal valve, and in the sinus of the ventral valve, 

 are undivided throughout their whole length. On each side of the fold and sinus the ribs 

 are bifurcated at various points between the beak and front margin. 



In one specimen, from which the shell has been partially removed, the cast of the 

 interior of the dorsal valve shows a mesial septum extending about one third of the length 

 from the beak. 



Length of a specimen of average size, thirteen lines; width, sixteen lines; depth of 

 both valves, nine lines. 



This species seems to be rare, as only about a dozen specimens have been collected. 



This is a well defined species of which we have observed but a single 

 typical example. 



Locality. Grande Greve. Billings's specimens are from Indian Cove. 



