206 GENESIS OF THE ARIETID. 
pressure. The keel is low and broad, as in odtuswm, though prominent enough 
to show above the lateral ridges when seen from the side. D’Orbigny’s figure of 
obtusum is correct, and gives this variety as it occurs at Semur, the abdomen 
| sometimes being wider than the dorsum, instead of being narrower than or 
i about equal to the dorsum, as in all other varieties. 
| There is a normal specimen of this species in the Museum at Stuttgardt, col- 
lected in the Upper Bucklandi bed ‘at Géppingen. The majority of specimens, 
however, belong to the Obtusus bed just above this. 
Confusion, as remarked above, is not infrequently occasioned by the resem- 
blances of the senile stages in Cor. Bucklandi to the adults of obtusum and Brooki. 
Sometimes even old specimens of Cor. trigonatum and G'muendense are mistaken 
by paleontolongists of experience and reputation for ob/usum, especially if the 
inner whorls are concealed. The larger and older specimens of od/uswm are apt 
to acquire the more abrupt umbilical shoulders which are characteristic of the 
| young and adult of Ast. stedlure. 
Asteroceras stellare, Uyarr. 
Plate IX. Fig. 2, 3. Plate X. Fig. 1, 2- 
Amami. stellaris, Sow., Min. Conch., I. p. 211, pl. xciii. 
Anm. stellaris, Z1utT., Verst. Wiirt., p. 15, pl. ii. fig. 5 
Amm. Brooki, Quenst., Amm. Schwab. Jura, p. 116, pl. xv. fig. 2, 3 (not pl. xx., xxi). 
Ariet. Brooki, Wricut, Lias Amm., p. 295, pl. xxii. fig. 1-6. 
Amm. obtusus suevicus, QuENST., Amm, Schwab. Jura, pl. xx. fig. 1. 
Localities. —Semur, Lyme Regis, Gmiind, Tiibingen. 
The nealogic stages are similar to the older ephebolic stages of var. E of Ast. 
obtusum. In point of fact, the two forms run into each other by intermediate 
varieties, and can be separated only by artificial lines. The young in one 
i specimen from Whitby exhibited on the first quarter of the fifth volution 
channels as deep, keel as prominent, and an abdomen considerably narrower 
than those of the most highly modified forms of Ast#. obtusum, var. E, on the last 
quarter of the sixth whorl, over a whorl and a half later. In a specimen from 
Lyme Regis the development is parallel with that of od¢usum, var. 1K, until the 
first quarter of the sixth whorl, then the sides became flattened, the pile de- 
pressed, and the abdomen narrowed to the area of the channel ee 
Sowerby’s types, figured by Wright, are young specimens, and exhibit very 
completely the fact that the young may develop the characteristics of the species 
at a comparatively early stage, and are more highly modified as a rule than the 
adults of obfusum in any variety. 
The sutures on the sixth volution of a specimen from Gmiind had lobes differ- 
ing two thirds and saddles one half; and on last quarter of same, the lobes differed 
three fourths and saddles two thirds. In an older specimen from Semur, on the 
second quarter of the seventh whorl degeneration had already begun, the lobes 
differing only one fifth to one sixth, and saddles about two fifths. This and the 
fold-like character of the pile and trigonal form showed that old age had fully 
begun on this whorl. There are two specimens of sfe//are in the Museum of Com- 
