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 striae. 



A dorsal valve measures, length 25 mm., breadth 30 mm.; a ven- 

 tral valve, length 23 mm., breadth 32 mm. 



This sj)ecies apparently belongs to that group of Orthis, in which 

 Prof. Jas. Hall has placed O. Vanuxemi, O. leucosia, 0. pcnelope and 

 O. cyclas of the Hamilton group of New York State, with the ciiar- 

 acters of which the new shell agrees quite perfectly in tlie 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 Maecurii, 

 and also found at the Rio Curuii locality. (Geol. Comm., 1876.) 

 Streptorhynchus Agassizii Hartt, MS. 



Rathbun, Bull. Buff. Soc. Nat. Sci., I, no. 4, p. 248, pi. ix, 1874. 



In the large collection of this species, made on the Rio Majcuru 

 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, Erere and the 

 Maecurii, are ver}' similar. Among the Maecurii specimens are ex- 

 amples in which the dorsal valve is more convex than is usually the 

 case with the Erere 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 



