4/8 



NORTH AMERICAN INDEX FOSSILS. 



LXXXIV. Anthracomya Salter. 



Differs from Naiadites in posterior end being produced, ex- 

 panded, and usually truncate. Hinge with narrow internal ridge 

 parallel with the edge of the valve in its posterior portion. Hinge 

 plate not striated ; an oblique diagonal ridge passes from the umbo 

 downwards and backwards. Differs also in being equivalve, with 

 larger and more conspicuous umbos. No byssal notch present. 

 Carbonic. 

 305. A. elongata Dawson. (Fig. 638, a, b.) Carbonic. 



Umbos less anterior than those of Naiadites carbonarius. 



Fig. 638. a, b, Anthracomya elongata, nat. size and enlarged ; c, d, A. Icevis, nat. 

 size and enlarged ; <?, Naiadites carbonarius. (After Dawson.) 



Nova Scotia, Cape Breton. 

 306. A. laevis Dawson. (Fig. 638, c f d.) Carbonic. 



Less oblique than preceding ; beak more nearly central. 

 Coal Measures of Nova Scotia. 



LXXXV. Nyassa Hall. 



Beaks small, anterior. Hinge line long and arcuate. Oblique 

 median depression and umbonal ridge often present. Surface 

 concentrically striated. Hinge with several irregular and coales- 

 cent teeth anteriorly and with 1 to 4 elongate lateral teeth pos- 



Fig. 639. Nyassa arguta. 



teriorly. Ligament external and inconspicuous. Pallial line 



simple. Devonic. 



307. N. arguta Hall. (Fig. 639.) Devonic. 



