438 G. C. Crick — Jurassic Cephalopoda — 



the latter differs considerably from that of the Australian species. 

 Ammonites polyptychus,^ Keyserling, resembles the Australian species 

 in its external form, but is distinguished by its dichotomoiis ribs 

 and the form of its suture-line. Ammonites arhustigerus,^ d'Orbigny, 

 occurring in the Bathonian of France, is a closely allied species ; 

 but the Australian form is distinguished by the greater prominence 

 of its shoi't umbilical ribs, by its finer sculpture, and by its suture- 

 line. The sculpture of the shell and the form of the suture-line 

 distinguish the present species from the form figured by d'Orbigny 

 as Ammonites planula ^ from the Bathonian of France. 



Localities. — Champion Bay; Cape Eiche, E. of Albany, Western 

 Australia. 



Ammonites (PerispMnctes) rohigtnosus, sp. nov. (PI. XIII. 

 Figs. 3 a and b.) 



Although a complete diagnosis of the species cannot be given the 

 following characters may be noted : — 



Shell (cast) discoidal, rattier widely umbilicated ; its greatest thickness at a short 

 distance from the inner edge of the whorl, about two-sevenths of the diameter of the 

 shell ; height of outer whorl about equal to its thickness. Umbilicus wide, probably 

 about three -sevenths of the diameter of the shell in width. Whorl obtusely cordate 

 in section, about as wide as high ; indented to about one -fourth of its height by the 

 preceding whorl ; periphery rather broadly convex ; sides somewhat flattened, 

 sloping away from the periphery ; inner area sloping towards the umbilicus. The 

 cast is ornamented 'with a number of primary umbilical ribs, or very compressed, 

 elongated tubercles, having a decided forward inclination ; each primary rib divides 

 into three secondary rounded ribs, which cross the periphery without interruption, 

 and are separated by interspaces of rather more than their own width. 



BemarTcs. — This species is represented by a portion of the outer 

 "whorl of an example of about 160 or 170 mm. in diameter. It is 

 a natural cast in a ferruginous matrix ; one side is fairly well 

 preserved ; the other is crushed and much weathered. It exhibits 

 no trace of the suture-line. Its extreme length measured along the 

 median line of the periphery is about 200 mm., the radius of 

 curvature of the periphery being about 86 mm. In a length of 

 173 mm. along the periphery there are 21 peripherial ribs, which 

 are connected with 7 primary ribs. The latter are about 12 mm. 

 apart, whilst the secondary ribs have a thickness of about 3 mm., 

 the interspaces being a little wider than the ribs. 



Affinities and differences. — The present species is very nearly 

 related to Ammonites Wagneri, Oppel,* from the Bathonian of 

 France, but the primary ribs of the Australian fossil are straighter, 

 moi'e prominent, and trifurcate more regularly. Compared with 

 d'Orbigny's figures ^ of Ammonites Fanderi, Eichwald, the present 



1 Petschora-Land, 1846, p. 327, pi. xxi. figs. 1-3; pi. xxii. fig. 9. 



^ Pal. Fran9. Terr. Jur. vol. i. 1842, p. 414, pi. cxliii. 



3 Pal. FranQ. Terr. Jur. vol. i. 1842, p. 416, pi. cxliv. According to Oppel 

 (Juraformation, p. 477), d'Orbigny's figure does not represent Hehl's Amm. 

 planula ; he, therefore, alters the naflie of d'Orbigny's species to Wagneri. 



* A. Oppel, Die Juraformation, 1856-58, p. 477 {_Ammonites planula, d'Orbigny, 

 Pal. FranQ. Terr. Jur. vol. i. p. 416, pi. cxhv. {non Hehl)]. 



^ D'Orbigny, in Murchisou, de Verneuil and de Keyserling, Geologie de la Russie 

 d'Europe et des montagnes de I'Oural, vol. ii. 1845, p. 430, pi. xxxiii. figs. 1-5 

 (figs. 1, 2 especially). 



