392 G. C. Crick — Jurassic Cephalopoda — 



The specimen from Western Australia figured by Moore as Am. 

 macrocephalus is preserved in the Bath Museum. It has a diameter 

 of 81 mm., but is so obscured by matrix that the other dimensions 

 cannot be made out, except perhaps the thickness, which at the right- 

 hand portion of the specimen as represented in Moore's figure is 

 31 mm. The very pronounced tubercle on the whorls gives rise to 

 two well-marked ribs, and there is occasionally an intermediate rib. 

 From the characters of the fossil, so far as they can be made out, 

 the specimen would seem to be referable to the present species. 



Affinities and differences. — Although resembling Ammonites 

 (Sphceroceras^) Woodwardi, the present species differs in having 

 a rather finer sculpture, less prominent primary (umbilical) ribs, 

 and a somewhat larger umbilicus. 



Unfortunately the suture-line of the Australian form is not avail- 

 able for comparison with other well-known species ; but the present 

 species is evidently closely allied to "Ammonites" Braihenridgii, J. 

 Sowerby (Min. Con. vol. ii. p. 187, pi. clxxxiv.). An example of 

 this species from the Inferior Oolite of Sherborne, Dorset (Brit. 

 Mus. No. 98239), in its external characters, agrees remarkably 

 well with the Australian fossil. It has the following dimensions : 

 diameter of shell, 57 mm. ; width of umbilicus, 26 mm. ; height of 

 outer whorl, 17 mm. ; thickness of outer whorl, 22 mm. ; with 

 27 umbilical, and 60 peripheral, ribs to a whorl. The present species 

 has finer ornaments and shorter umbilical ribs than d'Orbigny's 

 figure of Amm. Braihenridgii (Pal. Frang. Terr. Jur, vol. i. 1842, 

 pi. cxxxv. fif. 3, 4) ; and coarser, less numerous ribs, much shorter 

 umbilical ribs, and less inflated whorls than d'Orbigny's Amm. 

 linguiferus (Pal. Fran 9. Terr. Jur. vol. i. 1842, pi. cxxxvi.) ; whilst 

 the presence of a tubercle at the point of bifurcation of each umbilical 

 rib at once distinguishes the Australian form from such species as 

 Amm. biplex, J, Sowerby (Min. Con. vol. iii. p. 168, pi. ccxciii. 

 ff. 1, 2). 



Locality. — Champion Bay, Western Australia. 



Ammonites (StepJianoceras) , sp. (PI. XII. Figs. 5a, 6.) 



Since this species is represented merely by a fragment it is not 

 possible to give a complete diagnosis, but the following characters 

 may be noted : — 



Shell (cast) inflated ; greatest thickness at the margin of the umhilicus. Um- 

 bilicus rather wide. Whorl (at the base of the body-chamber) obtusely cordate or 

 almost lunate in section, nearly twice as wide as high ; indented to about one-fourth 

 of its height by the preceding whorl ; periphery broadly convex and continuous with 

 the sides ; inner area sloping steeply towards the umbilicus and forming an acute 

 angle with the convex surface of the shell. Sutm'e-line imperfectly known. "Whorl 

 ornamented with a number of umbilical transversely-compressed tubercles, situated 

 upon the prominent margin of the umbilicus ; each tubercle giving rise to three ribs 

 which, in crossing the convex surface of the cast, form a broad shallow sinus having 

 its concavity directed backward. The tubercles are not continued over the inner 

 area of the whorl. 



Remarks. — The fragment representing this species is a natural 

 cast in a ferruginous matrix of a portion of the body-chamber and 

 of the adjoining chamber, the form of part of the penultimate 



