1878.] 23 (Rathbun. 
fourth that of the valve, or slightly more. The socket plates of the 
dorsal valve extend in about the same direction, or diverge slightly 
more, but they are not as long as the lamellae. Cardinal process 
not preserved. 
Shell marked with fine, closely arranged, radiating raised lines, 
which are of about the same width as the depressions separating 
them, or slightly broader. ‘They appear to increase in number most- 
ly by intercalation. An elliptical specimen measures, length 15 mm., 
breadth 21 mm.; a nearly circular one, length 15 mm., breadth 
16 mm. ; 
This species belongs to the type of Orthis lenticularis, of the Upper 
Helderberg Group of New York, though specifically it does not re- 
semble any N. American form. It is represented in the Devonian 
sandstone of Ereré by only a few very small specimens; many speci- 
mens of larger size were, however, obtained from the Rio Mecuru. 
Two or three small specimens were found in the sandstone of the 
Rio Curud. (Morgan Exs., 1870 and ’71; Geol. Comm., 1876.) 
Orthis Harttii, sp. nov. 
Shell of nrediuin to large size, transverse, subplano-convex, or with 
the ventral valve slightly convex on the umbo. Dorsal valve broad- 
ly subovate in outline; ventral, transversely subelliptical. Hinge 
line short, equal to about one-third to one-half the width of the 
shell. Surface marked with fine, radiating raised lines. 
Ventral valve broadest near the middle; proportions of length to 
breadth about as 2 to 3, or length and breadth nearly equal. There 
is an undefined, shallow, and rather narrow, median sinus, which causes 
a slight indentation in the anterior margin of the valve. It com- 
mences some distance forward of the beak, and is often scarcely de- 
veloped at all. Beak of medium size, prominent and acutely pointed, 
and projecting a short distance beyond the hinge line. The sur- 
face of the valve curves up rapidly from the hinge line toward the 
middle of the valve, but all the median and anterior portion of the 
valve is broadly flattened, and at times depressed to form the sinus. 
Dorsal valve moderately convex, and broadest just anterior to the 
middle, the margins curving rapidly outward and forward from the 
beak to the point of greatest width, in front of which the margins 
form a regular curve, so that, as a rule, the valve has quite a perfect, 
broad-ovate outline. Along the median line the valve is usually 
broadly, but not strongly, elevated in an undefined prominence, 
reaching from near the beak to near the front of the valve. This el- 
