CEPHALOPODA. 309 



along the last air-chamber is rapidly expanded, becoming cylindrical through- 

 out the greater length of the grand chamber, and contracted at the aperture. 

 Aperture oblique to the axis of the tube. Air-chambers regular, having a 

 depth of 3.5 mm. Those near the outer chamber are somewhat shallower, 

 but the change in depth towards the apex is very slight. 



Septa thin. The other characters of the septa and those of the siphuncle 

 have not been observed. Sutures curved and oblique to the axis, at an angle 

 of about 70° along one side of the tube. 



Test not preserved. The surface-markings upon the internal mould are 

 curved, transverse, lamellose stria}. 



The specimen figured, which is nearly entire, has a length of 113 mm., of 

 which thirty-three mm. pertain to the grand chamber, with a diameter at 

 the aperture of twenty-three mm., and embraces twenty-eight air-chambers. 



This species is distinguished by its rapidly enlarging tube, and the curvature 

 and obliquity of the septa. It somewhat resembles O. Leander, but the tube is 

 more rapidly enlarging, the air-chambers shallower, and the sutures are oblique. 

 The regular curvature and obliquity of the sutures give the specimen a spiral 

 appearance, which is very characteristic. 



Formation and locality. In sandstones of the Chemung group, at Warren, Pa. 



Orthoceras Leander, n. sp. 



PLATE XC, FIGS. *-B. 



Shkll straight, regularly and rapidly enlarging from the apex to a point near 

 the aperture. Transverse section subcircular. Apical angle Hi . Initial 

 extremity unknown. 



Chamber of habitation, with a length of twice the diameter of the tube at 

 the last septum ; regularly expanding to the aperture, where the tube is 

 slightly contracted. Air-chambers showing a slight variation in depth in 

 different individuals, varying from three to five mm. The last air-chamber 

 Imllower than the preceding, but the variation towards the apex is very 

 slight. 



