Rathbun.] 24. [May 15, 
evated portion is rounded on top, or is marked by a faint longitudi- 
nal depression. It broadens rapidly forward, at the same time de- 
creasing in height; near the middle of the valve its width equals about 
one-third that of the valve, or a little more; at the front it is one- 
half the width of the valve; at the sides it rounds over rapidly to- 
ward the lateral and posterior margins. Beak small and pointed; 
hinge area short, triangular. . 
In the interior of the dorsal valve there exists a rather small, but 
prominent and projecting, cardinal process, and moderately heavy 
dental plates, which latter diverge at an angle slightly less than a 
right angle. Septum broad, very slightly elevated, and reaching 
nearly to the middle of the valve. Muscular impressions of the ven- 
tral valve large and extending beyond the middle of the valve. 
They broaden rapidly from the beak forward, attaining their 
greatest breadth near the front, which is slightly rounded. A medi- 
um-sized septum separates them to the front. Surface marked with 
fine, closely placed, radiating raised lines which are sometimes slight- 
ly broader, at others slightly narrower, than the intervening striz. 
A dorsal valve measures, length 25 mm., breadth 30 mm.; a ven- 
tral valve, length 23 mm., breadth 82 mm. 
This species apparently belongs to that group of Orthis, in which 
Prof. Jas. Hall has placed O. Vanuzxemi, O. leucosia, O. penelope and 
O. cyclas of the Hamilton group of New York State, with the char- 
acters of which the new shell agrees quite perfectly in the dorsal 
valve, and also in the ventral valve, excepting that the latter is some- 
times proportionally broader than the dorsal. 
Quite abundant in the Devonian sandstone of the Rio Mezcuri, 
and also found at the Rio Curué locality. (Geol. Comm., 1876.) 
Streptorhynchus Agassizii Hartt, MS. 
Rathbun, Bull. Buff. Soc. Nat. Sci., 1, no. 4, p. 248, pl. Ix, 1874. 
In the large collection of this species, made on the Rio Mecurt 
by the Geological Commission in 1876, there are to be noted only a 
few variations beyond those already recorded in the original descrip- 
tion of the species. The forms from the two localities, Ereré and the 
Mecurt, are very similar. Among the Mecurti specimens are ex- 
amples in which the dorsal valve is more convex than is usually the 
case with the Ereré forms, and the beak of the ventral valve is some- 
times more elevated. The dental plates at times reach forward a 
short distance into the valve, and the cardinal process is generally 
