430 



NATURAL SCIENCE. 



Dec. 



Fig. I. 



Fig. 2. 



Fig. 3. 



Fig, I — Bactrites. a. A shell retaining the protoconch and showing the expansion 

 of the initial tube and the ornamentation {B. cf. gracilis), x 16. h. The distal 

 surface of the first septum (somewhat broken), in B. aciculum, showing the lateral 

 position of the siphuncular passage. The margin of the septum on the left is the 

 line between light and shade. x 50. c. Interior of a portion of the shell of 

 B. cf. gracilis, showing the intra-marginal position of the septal necks. X4. 

 d. Dorsal view of an internal calcareous cast of B. cf. gracilis showing the usual 

 lobed appearance of the sutures, x fl. 



Fig. 2. — OrtJioceras (?), from Genesee shales, a. First septum, seen from above, 

 showing central siphuncular passage, x 29. b. Protoconch and first loculus. 



X35- 

 Fig, 3. — Na7ino aulema. a. Vertical longitudinal section of the apical portion of the 

 infilling of the siphuncular passage and protoconch ; a. the internal cavit)' ; 

 b. calcite lining, with a streak indicating pause in deposition. b. A similar 

 specimen seen from the exterior, showing swollen smooth apex and annulated 

 siphuncular tube. c. The most complete example observed, showing siphuncular 

 tube on left, constricted where it passed through the septa, lower down some 

 septa, and then the conical apex. All x 1.3. 



(All these figures are adapted from J. M. Clarke.) 



