part 1] ON THE MOEPHOLOGY OF THE AMMONITE SEPTUM. 31 



III. Materials used in the Inyestigation. 



Three species of ammonites were chosen for the main pai*t of 

 this enquiry, namely : — 



Dactylioceras cominune, because it had what may be defined as a 



normally shaped whorl : that is, neither depressed nor compressed 



to- any marked degree. 

 Sphseroceras hrongiiiarti, as an example of a form possessing a depressed 



whorl. 

 Tragojilxxjlloceras loscomhi, as representing forms possessing elevated and 



compressed whorls. 



In the two former the development of the sutm*e was worked 

 out in the same specimens as those from which the septa used for 

 making septal sections were taken. In the first, a series of septa 

 was also cleaned, while the protoconch and first whorl were re- 

 constructed in wax, and arranged in such a w^ay that the separate 

 chambers could be taken apart and the septa examined. 



Fig. 3. — Grcqyh sliowing the average j)rofile of ill e adult septum 

 o/' Dactylioceras commune (see PI. Ill, Jig. 1). 



-3 - 



\. 





Datum-pla 



ne 





■ 







-\ 



•o 





















o 





















l^ 









o \ 



of anterio 



u 



CIS 



♦a 

 o 









<U 



n! 







I 



< 



u. 



. 



^ 



< 



Area in front of successive contours. 



We are indebted to Mr. W. D. Lang, F.G.S., of the British 

 Museum (Natural History), for samples of the third, and we relied 

 for the sutm^al development upon the figures of Mr. L. Spath,i 

 which we reproduce here in fig. 12 (p. 46). The details of other 

 material will be given below. 



IV. The Morphology or the Adult Septum. 



The consideration of the morphology of the septum may be 

 approached from a study of the contoured plan (fig. 4), which was 

 made from a cleaned septum of an adult Dactylioceras commune. 



^ ' On the Development of Tragophylloceras loscombi ' Q. J. G. S. vol. Ixx 

 (1914) p. 341. 



