PACKARD. — RHODE ISLAND CARBONIFEROUS. 



401 



Valley Falls. In this specimen there were about a dozen casts of 

 valves of old and partially grown shells with the shape and markings in 

 some cases well preserved owing to the fineness of the shale. Another 

 specimen showing well the shape of the valves was detected in the black 

 shaly plant-beds enclosing a vein of coal just north of Silver Spring, East 

 Providence, by Prof. F. P. Gorham, associated with the verticillate leaves 

 apparently of Calamites. In these specimens the valves are elliptical, 

 long, narrow, pod-like, the anterior end but little larger and rounder than 

 the posterior end. The umbones are situated at or between the anterior 

 ^ and £ of the shell. There are about twenty-five fine lines of growth. 

 The fully grown specimens are narrower than the young and the anterior 

 is but little larger and rounder than the posterior end. Size and 

 proportions of the largest examples : length 22 mm., breadth 9 mm., being 

 about 2.V times as long as wide. Length of the East Providence 

 example, 17 mm.; breadth, 9 mm. In this example the umbones are 

 situated near the anterior fourth of the valve. The young in the loose 

 boulder were 10 mm. in length, 5 mm. in width, or one-half as wide as 

 long, with numerous fine lines of growth. 



Figure 1. — Anthracomya arenacea. X 2f. u, umbo. 



The Rhode Island specimens present no differences from the descrip- 

 tion and figures of Dawson (Acadian Geology, 3d edit., p. 205). It is an 

 entirely different species from Naiadites elongatus and laevis Dawson, of 

 vol. xxxv. — 20 



