78 ME. G. C. CRICK ON THE MUSCULAE ATTACHMENT OF THE 



become firmly attached to the shell. The anterior faintly-impressed line may have been 

 the last attachment of the anterior boundary of the shell-muscle during the gradual 

 growth of the animal upward prior to the formation of a new septum. The corresponding 

 line on the left side is obscured by the shelly matter adhering to the cast. 



On the median portion of the peripheral area the septum j^ossesses a rather broad 

 (median) saddle, on either side of which is a small lobe — the two halves of the peripheral 

 lobe. This is followed by the peripheral or external saddle. Anterior to the septum and on 

 the central portion of the same area there is a feebly -incised line having the form of half 

 an ellipse (PL 17. fig. 3) ; it arises close to the outer portion of the external (or peripheral) 

 saddle, i. e. at about 7 mm. from the median line of the siphonal (ventral) area ; then curves 

 upward and towards the median line, attaining its greatest height at about 8'5 mm. in front 

 of the median saddle, or about 5'5 mm. from its commencement. The line seems then to 

 pass on to the other side without interruption, but the surface of the cast is not sufiici- 

 ently well preserved to enable this to be stated w4th certainty. Its anterior portion is 

 about on the same level as the anterior portion of the boundary of the muscular impression. 

 About 6 mm. in front of this curve there is a similarly-curved feebly-impressed line, w'hich 

 inost probably is comparable with the faint curve on the opposite (antisiphonal) surface. 



Although the annulus is not well shown in this example, there is another specimen 

 [C. 5415 Jj] in the British Museum, from the same horizon and locality (PI. 17. fig. 4), 

 which displays the muscular impression less distinctly, but clearly shows the anterior 

 boundary of a portion of the annulus. This leaves the muscular impression at the " angle " 

 mentioned in the previous description, and, passing upward over the adjoining saddle 

 at a distance of about 1*5 mm. from the siiture-line, crosses the next lobe in a shallow 

 depression, arid again rises over the next saddle iit about the same distance from it as 

 before. This depression, however, is seen only with difficulty and by turning the specimen 

 about in a fairly good light. There can, I think, be no doubt that the annulus was in 

 the form of a simply-w^aved band, being elevated at the saddles and very feebly depressed 

 in each lobe just as in the example of Cardioceras excavatum already described (p. 75). 

 The total length of the specimen is 245 mm., the body-chamber (the aperture of which 

 is not preserved) occupying 165 mm., the diameters of the base of tlie body-chamber 

 being 44 and 31"5 mm. respectively. The other side of the cast of the body-chamber is 

 obscured by fragments of the test. 



BacHlites vagina , Porbes. — A portion of the muscular impression has also been seen 

 in an example of this species in the British Museimi Collection [one of the specimens 

 numbered 83624] from the Upper Cretaceous of Pondicherry, India (PI. 17. fig. 5). It is 

 merely the internal cast of the greater portion of the body-chamber, about 60 mm. long, 

 anteriorly incomplete, but fairly perfect posteriorly. Its transverse section is oval, the 

 diameters of its antei-ior end being 24 and 145 mm. ; those of the posterior end being 

 19 and 12-5 mm. The antisiphonal surface is broad and slightly flattened, the siphonal 

 being narrow, flattened, and with suliangular borders. On the broad antisiphonal svu-face 

 the feebly convex boundaries of the two muscular scars (indicated by a feebly-incised line 



