LOWER HELDERBERG ROCKS, 343 



circular, the shortest diameter being between the ventral and dorsal 

 sides. Septa numerous, approximate, very gently concave ; outer cham- 

 ber deep. Siphuncle dorsal, somewhat moniliform or constricted at its 

 passage through the septa ; internally marked by sharp elevated longi- 

 tudinal striae, the impressions of which are preserved in casts of the 

 interior. Surface unknown. 



I have seen only casts of imperfect specimens of this species, and in none of 

 these is the apex preserved. Although but slightly curved, the specimens are uni- 

 formly so; and one or two fragments, from near the apex, show a greater curvature 

 in that part than below. 



Fig. 3 a. A cast preserving a part of the outer cliamber and about twenty septa. Tlie back 

 is somewhat worn, so that the form of the siphuncle is seen. 



Fig. 3 6. Lateral view of a fragment of a larger individual, showing the cast of the interior 

 of the siphuncle. 



Fig. 3 c. A smaller individual, lateral view. The apparent rapid attenuation above is due to 

 compression of the lower part of the specimen. 



Fig. 3 rf. A portion of the cast of the siphuncle, with the filling between the adjacent septa. 

 The matter filling the siphuncle does not apparently differ from that filling 

 other parts of the fossil j but it has been deposited between thin elevated la- 

 mellae originally forming part of the walls of the siphuncle, and which, with all 

 the shelly matter of the specimen, has been removed. 



Geological position and locality. In the upper part of the tentaculite limestone : 

 Herkimer county. 



Ortlioceras lon^canieratuiii ( n. s.). 



Plate LXX. Fig. 1 ; and Plate LXXI. Fio. 1 & 5. 



Shell elongated, very gradually tapering; chamber extremely elongated. 

 Septa numerous, highly arched, about four or five in the space of the 

 diameter of the shell. Siphuncle moniliform. Surface unknown. 



The specimens of this, and of all the other species in the rocks of this age, are 

 so obscure as to afford barely the means of specific distinction. The species under 

 consideration is remarkable for the long outer chamber and the highly arched septa. 



PLATE LXX. 

 Fig. L The siphuncle has been filled with crystalline matter, and the swollen portions are 

 concave above and beneath, indicating a thickening of the septum at its junction 

 with the narrower parts of the siphuncle. Some remains of the septa are still 

 perceptible. 



