G. C. Crick — On Ammonites calcar. 557 



apparent, and this, together with Zieten's statement that Ammonites 

 bipartitus also came " aus dem ixntern Oolith uuvveit Gnttenberg," 

 suggests a possible relationship between the two forms. This 

 apparent relationship is confirmed by the comparison of Zieten's 

 type of Amm. calcar with a normal example of his Amm. bipartitus^ 

 of which species there are several German examples ' in the British 

 Museum collection. Several other differences are apparent besides 

 the arrangement of the tubercles on the periphery. Thus, compared 

 with an example of Zieten's Amm. bipartitus of about the same size, 

 Amm. calcar has more inflated whorls and a slightly smaller 

 umbilicus. This is clearly shown by a comparison of the 

 dimensions of the specimens. Thus the measurements of Zieten's 

 type-specimen of Amm. calcar are: — Diameter of shell (excluding 

 spines), 20-5 mm. (100); width of umbilicus, 4-5 mm. (21-9) ; 

 height of outer whorl, 10 mm. (48*7) ; height of outer whorl above 

 preceding whorl, 8 mm. (39-0) ; thickness of outer whorl, 

 7*5 mm. (36-5) : whilst the dimensions of an example of Zieten's 

 Amm. bipartitus from the Brown Jura ^, Beuren, Wiirttemberg 

 [C. 7,267&] at the same diameter are: — diameter of shell (excluding 

 spines), 205 mm. (100) ; width of umbilicus, 5 mm. (24'3) ; height 

 of outer whorl, 9'5 mm. (46"3) ; height of outer whorl above 

 preceding whorl, (?) ; thickness of outer whorl, 7 mm. (34-1) : and 

 the dimensions of a smaller but slightly more inflated example 

 [22,3246] of the same species are: — diameter of shell, 19-5 mm. 

 (100) ; width of umbilicus, 4-5 mm. (23 '0) ; height of outer whorl, 

 9 mm. (46-1) ; height of outer whorl above preceding whorl, 

 7 mm. (35-8). 



Compared with that of Amm. bipartitus, the suture-line of Amm. 

 calcar, besides being unsymmetrical, presents slight differences in 

 its details (compare Figs. Id and 2), but all these may, we think. 



Fig. 2. — BonareUia hicostata, Stalil, sp. Suture-line of normal example for com- 

 parison with Fig. \d, the dotted lines near the middle of the figure indicating^ 

 the position of the row of tubercles on each margin of the periphery, and the 

 short curved lines at each end marking the position of the suture of the shell. 

 BrowTi Jura ^ (Lower Oxfordian) : Balingen, "Wiirttemberg. Drawn of twice 

 the natural size from an example in the British Museum (Natural History) 

 collection [39,926]. 



be attributed to the general deformation of the specimen. As might 

 be expected the greatest difference is in the peripheral portion of 

 the line ; the peripheral saddle on each side, especially that on the 

 right in Fig. Id, is much reduced in width, but it, nevertheless, 

 exhibits a subdivision which is clearly comparable with that of the 

 corresponding saddle in Amm. bipartitus. 



1 There are four examples (22,324ff-(?) from the Brown Jura f , Beuren, "Wiirttem- 

 berg ; one (39,026) from Balingen, Wiirttemberg; and four others (C. 7,267«-^> 

 from Germany, but the precise locality of these is not recorded. 



