1892.] NATURAL SCIENCES OF PHILADELPHIA. 139 



tact and then appear from the inner .side of the whorl on the 

 free outer surface, being exposed by the uncoiling of the shell. The 

 total number of main lobes and saddles of the adult shell is ap- 

 parently developed at the second septum, and the further develop- 

 ment of the suture consists in the formation of secondary lobes and 

 saddles, appearing as complexities of the primary or r^ain ones. Of 

 these secondary folds of the suture, the first to appear is the narrow 

 ventral saddle at the fourth suture, and probably also the narrow 

 dorsal lobe is formed but little later, for both are about equally well 

 marked when the shell passes into the straight form. The fact that 

 the adult number of lobes is developed at the second septum is an 

 evidence of cataplastic development, the adult number of lobes in 

 the suture being usually developed at a much later stage in the 

 normal coiled Ammonites. But in other uncoiled and degenerate 

 forms the niepionic lobes are retained throughout their development 

 and are not added to in the adult stages. 



The outer nacreous shell when preserved is found to be marked 

 by minute tuberculations of irregular shape; these in turn give 

 place to the parallel curved lines seen in the adult shell. These 

 parallel lines first appear about the fourteenth septum, and they 

 soon completely obscure the tuberculation. Between the first and 

 second sutures there is apparently an interruption in the growth of the 

 shell, appearing as a line resembling a suture line, PI. IX, fig. 

 10. This line seems to be slightly raised above the general shell sub- 

 stance; it extends over the end of the ventral lobe of the second 

 suture and back in a simple curve to near the lateral ends of the 

 first suture. In breaking away the nacreous shell substance to 

 show the sutures, the break nearly always follows this line, leaving 

 the protoconch covered by the original shell. Over the area thus 

 left of the original shell substance the tuberculations are found to 

 be more circular in outlineaud closer together than in the succeeding 

 portions of the shell. It is believed that the portion of the shell thus 

 bounded represents the original embryonic chamber, or protoconch 

 PI. IX, fig. 5, which would thus extend beyond the point where the 

 first septum was subsequently developed. A section in the plane of 

 the spiral, but not quite median, PI. IX, fig, 11, showed the shell 

 to be composed of successively deposited layers, and the first of these 

 was seen to extend a short distance beyond the first septum, thus 

 tending to confirm the above belief. It thus seems probable that 

 the outer limit of the protoconch lies between the first and second 



