140 PROCEEDINGS OF THE ACADEMY OF [1892. 



septa, as shown in PI. IX, fig. 10, The edge of this supposed em- 

 bryonic shell is seen to be finely crenate, but not regularly so, the 

 crenatures being larger in some parts than in others. On breaking 

 away the outer shell of the protoconch this line still persists and it 

 might readily be mistaken for a suture line, if it did not overlap 

 the lobe of the second suture. The section of the shell in the plane 

 of the spiral above referred to shows that there is no septum at this 

 point, but there is apparently a slight thickening of the shell sub- 

 stance. 



The protoconch, as seen in this section in the plane of the spiral, 

 PI. IX, fig. 11, is quite large and nearly circular, and of the gen- 

 eral form common to all of the Ammonoidea. The section not being 

 quite median the siphuncle is not shown, and the septa do not present 

 exactly the same form as they would in a median section. Only 

 one such section was ground on account of scarcity of material to 

 work on, but this one shows the structure to be that of the Ammon- 

 oidea in general. The septa were equally spaced, or nearly so, up 

 to the twelfth, from which point they are successively more widely 

 spaced. It is to be noted that at about this point the lateral con- 

 traction of the shell ceases and the gradual increase in lateral 

 diameter begins, apparently indicating a change in the conditions 

 of the life of the animal. 



After considerable investigation I have been unable as yet to 

 trace the phylogeny of this species. A careful examination of the 

 development of the shell in the earlier stages of Scaphltes conradi 

 Morton, a form associated with the young of Baculites in this same 

 material, showed that the Scaphites must have been derived from a 

 totally different stock, and cannot be related to Baculites. Nor do the 

 adult suture lines of the two forms show much resemblance to each 

 other. An interesting point was developed, hoAvever, in the study of 

 the young of the Scaphites, which tends to confirm my observation 

 on the extent of the first embryonic shell as shown in PI. IX, fig. 

 5. A very successful median section of Scaphites conradi in the plane 

 of the spiral showed a thickening of the shell at the termination of 

 the first layer, Avhich is between the first and second septa as in 

 Baculites, this thickening indicating an interruption in the growth 

 of the shell such as might be expected on the emerging of the young 

 from the egg. But this correspondence in the extent of the embry- 

 onic shell does not indicate a relation between the two forms, it 

 being a character probably common to all Ammonites. Indeed, 



