FIFIII. OB AG ISSICER \N BR V\< II. 207 



y, winch are bo similar to •/ that they differ it» only one 



characteristic, namely, the shallowness of the umbilicus, due to the gradual 

 curvature of the sides In l / the breadth of tin- dorsum, and the con- 



:it abruptness of the umbilical shoulders, is a marked peculiarity, even al 

 an earl} m These specimens were in the neal ; if older, 



they would probably also have shown a leas amount of involution than ii 

 / rhis last specie* becomes generally, though not invariably, larger in 



five volutions than the former in the course of five and a half. Specimens of 

 so approximate very closely t<> l ltum ; they differ, however, in 



the leas involution <>t' the whorls, and in other correlative characti 



Depressed tubercles similar to those of the young of ippeared, in the 



only specimen in which they could be detected, on the last quarter of the « 

 whorl, and inn- pilsB on the third quarter of the third whorl, earlier \>\ one 

 volution than in var. K i Thus even in this unimportant character 



ken place as it had in other charai 



There i- one specimen of this species in the Museum of Stuttgardt, from the 



Geometricus bed of Goppingen, though it is more common in the Obtusus bed. 



The largest specimen in this Museum reached a diameter of 150 mm. (PI. X. 



I _ The last whorl was perfectly Bmooth, the abdomen had become sub- 



. and the channel- obsolescent, resembling those of the adults of Ast. 



Astcroceras acceleratum, Btatt. 



i-i ... i\ i \f i. i 



•viimr 



involution cover- two fifths of the Bides on the sixth whorl, and one half 



of the second quarter of the eighth, whereas in ./>/. steUare the extreme limit of 



in vol i • e third. The whorl is similar to that of this species, but is much 



Inmino-dorsally. The umbilical shoulders are large and abrupt, the 



■ii much broader than the abdomen, the latter being but little wider than 



the area of the channels. The latter tire very broad and shallow, with si th 



but d< The heel is well marked, but depressed as in 



The abdomen i- therefore quite different from that of either U 



I //' until a late Me. i . and differ onlj in 



i involution of the whorls in later stages, and in the earlier develop- 

 ment ol the senile folds and trigonal form The umbilicus could be obsen 



only one specimen In this the pil fold the last q 



of the second whorl, which developed into true pilic on the first i the 



fifth whorl 



• n Ii Scmui inin.. and bad c pl< l< tl the 



ii, The breadth of the 



_dith whorl in. 77 nun. i n in 



II the 



