ANIMAL TO ITS SHELL IN SOME FOSSIL CEPHALOPODA. 107 



of the external saddle these lines diverg-e, assume a direction at right angles to the plane 

 of symmetry of the shell, and cross the external lohe with only a very sliglit V-shaped 

 depression at the median line of the periphery. jS'early at the centre of the peripliery 

 there is a small circular pit on the posterior lino. On the opposite side of the lobe, 

 at about 1 mm. from the suture-line, these lines turn aliruptly forward, approach and 

 coalesce, the resulting line having the same course as that on the opposite side. At the 

 umbilical margin this line passes into the boundary of the muscular scar, which also has 

 the same form as that on the opposite side. At the centre of the periphery and imme- 

 diately behind the lines already described there is a feebly-depressed double line in the 

 form of a horse-shoe, each side of which passes quite close to the outer side of each half 

 of the small median saddle; the enclosed area is about 2 mm. wide. At a short distance 

 anterior to the raised line already described there is a rather broad shallow groove, which 

 first makes its appearance in the lateral lobe, becomes more distinct all around the 

 external saddle, and disappears in the external lobe. Almost in the median line of the 

 periphery, and slightly in advance of the apex of the external saddle, there is a minute, 

 shallow, oval depression. A fairly-jirominent " normal line " extends some 7 or 8 mm. in 

 advance of this depression, whilst the surface of the cast behind this depression and in front 

 of the anterior boundary of the annulus bears numerous fine longitudinal raised lines. 



The depressed surface on the inner area of the whorl I regard as a portion of the 

 muscular scar, and the faint line proceeding therefrom across the whorl I consider 

 to be the impression of the annulus. The latter then seems to have been over a portion 

 of its extent merely a line of attachment, but to have been 1 mm. wide on the 

 periphery. 



In the present specimen the boundary of the muscular scar cannot be traced on to 

 the inner or dorsal poi'tion ( = impressed area) of the whorl, Init this has lieen partially 

 observed in another example of the same species in the British Museum Collection (the 

 larger of the specimens Xo. C. 283). The diameter of the shell is 50 mm., the outer whorl 

 (at the end of the septate part of the shell) being about one-half of the diameter. The 

 specimen is entirely septate (PL 20. figs. 17, 18), tlie last septum being the base of the 

 body-chamber. A portion of the test that formed the floor of the body-chamber still 

 adheres to the preceding Avhorl, and on this the border of the muscular scar can be traced 

 for a short distance. In this example the anterior border of the scar j^asses on to the 

 floor of the body-chamber at about 3"5 mm. in advance of the last sej)tum ; for a short 

 distance it is nearly parallel to the sejjtum, Imt at about the middle of the lateral saddle 

 it turns towards the septum and seems to disapjiear ; unfortunately the test here has 

 been broken away, and only a few fragments of the test remain on the opposite side of 

 the whorl, so that its direction cannot be definitely traced further. On the floor of the 

 body-chamber (fig. 18) there is also a strong raised line following the lobes and saddles of 

 the last septum, and about 1 mm. in front of the same ; near the umbilicus it gradually 

 approaches and then passes into the angle between the septum and the wall of the 

 shell. This seems to have been a line of attachment of the body of the animal ; but, so 

 far as can be made out from this example, it does not ajipear to have been continuous 



