from Western Audralia. 393 



septum being seen at the posterior extremity of the specimen. One 

 side of the cast is fairly well preserved ; the other is much crushed 

 and worn. The impressed zone, seen on the inner part of the whorl, 

 shows that the ribs of the preceding whorl crossed the periphery 

 without interruption. That the umbilicus was wide is indicated by 

 the direction of the tuberculated margin of the fragment ; this 

 margin has five tubercles in a length of 38 mm. The maximum 

 length of the specimen along the periphery is 80 mm. and its radius 

 of curvature is 67 mm. Seventeen transverse ribs can be counted 

 on the periphery ; the interspaces are of about the same width as the 

 ribs. The chamber adjoining the body-chamber was shallow, but, 

 as this chamber is frequently much shallower than the rest, it may 

 not represent the average depth of the chambers. The height of 

 the whorl is 33 mm., the height above the preceding whorl being 

 27 mm. ; the width was probably about 60 ram. 



Affinities and differences. — The species represented by this fragment 

 appears to be a close ally of Ammonites siiblcevis, J. iSowerby,^ from 

 the Oxford Clay and Kellaway Kock, having a particularly close 

 resemblance to the middle-aged shell of this species from the British 

 Callovian. But, judging from the fragment, the Australian fossil 

 had a larger umbilicus and less numerous umbilical tubercles, and 

 whilst in Sowerby's species the ribs arise usually in pairs from the 

 margin of the umbilicus, in the Australian specimen each umbilical 

 tubercle gives rise to three ribs. 



The whorls of Ammonites coronatus, as figured by d'Orbigny,^ 

 have a much coarser ornamentation, a broader and flatter external 

 area, and a narrower inner area than the Australian form ; whilst 

 Ammonites Atherstoni, Sharpe,^ from South Africa, as represented by 

 a specimen in the British Museum (No. 46534), has a smaller 

 umbilicus, smaller umbilical tubercles, and very distinct, forwardly- 

 directed ribs on the inner area of the whorls, i.e. on the sides of 

 the umbilicus. 



Ammonites Schenki, Oppel,* from the Jurassic of the Himalaya, has 

 a smaller umbilicus, much more prominent umbilical tubercles, and 

 less numerous peripheral ribs. 



^ In sculpture the Australian form resembles OlcostepTianus latis- 

 simus, Neumayr and Uhlig,^ but it is a less tumid shell, and, so far 

 as can be ascertained, has a different suture-line, its suture-line more 

 nearly resembling that of Ammonites Sutherlandice, J. de C. Sowerby,^ 

 from the Calcareous grit, but the character of the ornaments at once 

 distinguishes these two forms. The adult of the latter species is 

 smooth, and the ribs on the inner whorls have a different direction 

 from those of the Australian form. 



Locality. — Champion Bay, Western Australia. 



1 Min. Con. vol. i. p. 117, pi. liv. 



2 Pal. Fraii9. Terr. Jur. vol. i. 1842, p. 465, pi. clxviii. 



3 Trans. Geol. Soc. [2], vol. vii. 1847, p. 196, pi. xsiii. f. 1. 



* Pal. Mittheil. vol. ii. pi. 81, ff. ia-c. 



* Palaeontogr. vol. sxvii. (1881), p. lo8, pi. xxviii. 

 « Min. Con. vol. vi. p. 121, pi. dlxiii. 



{To he continued.) 



