ANIMAL TO ITS SHELL IN SOME FOSSIL CEPHALOPODA. 85 



AMMONITES *. 

 Amaltheid ,e, p. Fischer. 



OXYNOTICERAS, A. Hyatt. 



Oxynoticeras^ sp. — The example (PL 18. figs. 5, 6) apparently referable to this genus, 

 in Tivhich the form of the muscular attachment has heen observed, is from the Great 

 Oolite (Stonesfield Slate) of Stonesfield, Oxfordshire, and forms part of the British 

 Museum Collection (No. 36710). It has been labelled "Ammonites discus, .7. Sowerby," 

 but it is jjrobably not referable to Sowerby's species f , although its state of preservation 

 does not allow an accurate determination. It is a crushed, poorly-preserved, internal cast 

 lying loose on a piece of matrix. The greater part of the specimen is septate ; the body- 

 chamber has been broken across obliquely, but fortunately the posterior portion is 

 preserved. When complete the specimen probably was quite 145 mm. in diameter, and 

 its umbilicus about 22 mm. wide. The last half-whorl at least was occuj)ied by the 

 body-chamber, the base of which is o2"5 mm. high and about 10 mm. thick. The 

 anterior border of the muscular scar and of the anuulus can be traced across each side of 

 the specimen, but it is more distinct on that side (flg. 5) lying upon the matrix. Here the 

 anterior border arises from the suture of the shell at a distance of 115 mm. in advance 

 of the last septum ; after passing forward and outward for a short distance it turns 

 backward in a rather broad curve, and passes uninterruj)tedly across the body-chamber 

 in a i'airly straight line, which is almost parallel to the general direction of the last 

 septum, being in advance of the septum 15'5 mm. on the inner portion of the lateral 

 area and 21 mm. near the periphery, where it seems to turn backward a little, but this 

 appeai'ance may be due to the much-compressed state of the fossil ; it has no depressions 

 corresponding to the lobes of the suture-line. The portion of the border to a distance of 

 about 13 mm. from the inner edge of the whorl is indicated by a well-marked depressed 

 line, and the rest of the border is indicated by the anterior boundary of a band of colour 

 about 4-5 mm. wide, the posterior boimdary of which is not sharply defined. The inner 

 portion, bounded anteriorly by the depressed line, doubtless rejn-esents the muscular scar, 

 and the broad band of colour the anuulus ; the scar exhibits distinct lines of growth. 



On the opposite side the muscular scar and annulus are less clearly defined. The 

 muscular impression appears to be somewhat nearer the last septum, for its anterior 

 boundary arises as a faintly-incised line at a point only S'5 mm. in advance of the last 

 septum, and passes outward and backward as far as the septum, wliich it meets at a 

 distance of 8'5 mm. from the inner edge of the whorl. Before reaching the septum, 

 i. e. at a distance of 3-5 mm. from the septum, this boundary gives off a branch (indicated 

 by a line of colour) which can be traced as a slightly- waved line across the body-chamber 

 to the periphery, where it meets the anterior boundary on the opposite side. The 

 portion of the annulus adjoining the muscular impression ou this side is only about 



* The nomenclature and grouping of the Ammonites here adopted are those given by Prof. Dr. K. A. v. Zittel in 

 his ' Grundzuge der Palaontologie," 1895. 



t J. Sowerby, ilin. Con. vol. i. p. 37, pi. xii. (1813). 



