ANIMAL TO ITS .SHELL IN SOME FOSSIL CEPHALOPODA. 75 



Animlus. 

 The impression of the annuius lias been observed in several specimeDS, but in the 

 British Museum Collection (No. C. 6801) there is an example of Cardioceras excavatimi 

 (J. Sowerby) * from the Oxford Clay, but the locality is not recorded, in whicli the form 

 of the miiscular attachment, and particularly that of the annuius, is remarkably well 

 displayed (PI. 18. fig. 8). The specimen is apparently complete, and shows the aperture 

 of the shell, which is provided with a narrow, ventral (or peripheral) apophysis. Its 

 dimensions are : — Diameter of shell 120 mm. ; width of umbilicus 21 mm. ; height of 

 outer whorl 58 mm. ; ditto above preceding- whorl 40 mm. ; thickness of outer whorl 

 about 43 mm. The body-chamber occupies the last half of the outer whorl, its base 

 being 44 mm. high and 29 mm. wide or thick. The whorl is subsagittate in transverse 

 section ; its inner margin slightly overhangs the umbilicus, so that the width of the 

 umbilicus, measured at the umbilical margin, is less than that measured at the suture of 

 the shell. A greater part of the test is preserved, and this is mostly in a soft friable 

 condition. Some of it had been removed from the left t side of the specimen, so as to 

 expose a portion of the internal cast of the base of the body-chamber. By means of a 

 small stiff brush the rest of the test was carefully cleared from both sides of the base of 

 the body-chamber, and the form of the muscular attachment of the animal was displayed 

 very clearly, especially on the left side, the attachment on the right side being jjreciselv 

 similar, but a little less distinct. On the left side the impression of the anterior boundary 

 of the shell-muscle crosses the umbilical margin 5 mm. in advance of the last septum, and 

 passes as a very narrow l)and of a. thin film backward and outward in a flat forwardly- 

 convex curve as far as the middle of the second lateral lobe, at which point, and 1"5 mm. 

 posterior to it, there is seen to be another similar band Avhich passes from the mnbilicus 

 immediately above the saddle on the margin of the umbilicus ; these two bands, con- 

 tinuing at abou.t the same distance apart, pass over the lateral saddle into the first lateral 

 lobe and, then diverging slightly, pass over the peripheral or external saddle forward and 

 outward towards the jjeriphery in a flat forwardly-convex curve, but becoming very 

 indistinct before reaching the periphery. These two very narrow filmy bands appear to 

 l3e the remains of the anterior and posterior boundaries of the annuius respectively. 



Remains of the annuius are visible also on the right side, but much less distinctly ; 

 they are, however, sufficiently clear to confirm the structures which have been mentioned 

 as existing on the left side. 



Having described the usual form of the muscular scars and of the annuhis, I now 

 proceed to describe their remains in various forms of Ammonoids, commencino" with the 

 genus Bactilites and proceeding in the order already indicated {ante, p. 73). 



* J. Sowerby, Min. Con. voL ii. p. 5, pL cv. (1815). 



t The terms " right " and " left " are used in a strictly morphological sense, the periphery (or siphoual area) of au 

 Amnionoid being ventral, and the anti])eripheral (or autisiphonal) area dorsal. 



