PLATE II. 



Cal. carusense. 1 Fig. 1, specimen reduced to one third, showing incomplete living cham- 

 ber and old age. Fig. 2, the same broken so as to show sections of the old whorls and the 

 depressed abdomen of the adult stage. Fig. 3, enlarged adult sutures, also shown on Fig. 1. 

 Fig. 3 a, same, but very old, also shown on Fig. 1. Loc. Semur. 



Arn. miserabile. Fig. 4, large smooth specimen, with sutures and incomplete living 

 chamber. Fig. 5, cast with sharp abdomen and gibbous sides, living chamber incomplete. 

 Fig. 6, enlarged sutures of the same. Fig. 7, var. cuneiforme, with incomplete living chamber. 

 Loc. Semur. 



Arn. obtusiforme. Fig. 8, section of a cast, showing form of internal whorls. Fig. 9, 

 specimen with incomplete living chamber. Fig. 9 a, enlarged sutures of fig. 9. Loc. Semur. 



Arn. semicostatum. Fig. 10, variety with incomplete living chamber, the young remain- 

 ing' smooth until a late period of growth and ribs immature, loc. Semur. Fig. 11, cast, with 

 ribs earlier developed than in Fig. 10, and slightly more prominent. Fig. 12, young from 

 same blocks of limestone. Fig. 13 a, sutures from other young specimens on the same block, 

 of different ages, all natural size. Loc. Whitby. Fig. 14, cast with folds in the extreme young 

 stage and true pilae beginning afterwards ; otherwise the form is perfectly normal, loc. Basle. 

 Fig. 15, normal variety with deep channels. Fig. 15 a, suture of the same, enlarged. Fig. 16, 

 specimen with incomplete living chamber, channels developed at an earlier age than in normal 

 variety, and abdomen broader and flatter in proportion than is usual in the species at any age. 

 Loc. Semur. 



Arn. Hartmanni. 2 Fig. 17, cast, loc. Bonnert. Fig. 18, suture of the same, enlarged. 



Am. tardecrescens. Fig. 19, cast of a young specimen with incomplete living chamber. 

 Fig. 19 a, enlarged suture. Loc. Yorkshire. 



Arn. ceras. Fig. 20 and 20 a, specimen with incomplete living chamber, a very broad 

 abdomen, and deep channels, loc. Semur. 



Arn. tardecrescens. Fig. 21 and 22, sutures of a specimen of a normal form (abdomen 

 narrower than the last), at the diameters of 63 mm. and 83 mm. Loc. Semur. 



Arn. Bodleyi. Fig. 23, broken specimen, showing planorbis-like folds on the young shell, 

 with living chamber incomplete. Fig. 24, more involute variety with similar fold in the young 

 and incomplete living chamber. Fig. 24 a, suture of the same, enlarged. Loc. Semur. 



Arn. falcaries. Fig. 25, young with slight tubercles on the geniculae. The last quarter is 

 part of the living chamber. Fig. 26, larger specimen, ribs not tuberculated or arising from, 

 tubercles as in the above, and keel very prominent. Fig. 27, cast with deep channels and abdo- 

 men very narrow. Loc. Semur. 



Arn. kridioides. Fig. 28, specimen showing the smooth young, the early period at which 

 the pilae begin, and the similarity of the umbilicus to that of a normal species of Arnioceras. 

 Loc. Basle. 



i See Plate I. Fig. 15, 16. 2 See PI. III. Fig. 1,1a. 



