208 GENESIS OF THE ARIETID. 
Geometricus bed, and one, broken across, from the Obtusus bed at Balingen. 
The last (Pl. X. Fig. 3) shows the young with shallower channels and flattened 
sides, somewhat similar to Ast. obfusum at an older period! The sides of the 
young, however, are flatter and broader than I have yet seen in any variety of 
stellare, and more like those of an aged Cor. trigonatum. The characteristics of 
the nealogic stages and of the adult are evidently geratologous. This spe- 
cimen is 258 mm. in diameter, The whorl of the adult is smooth, and of same 
shape as the senile stage of Ast. obtusum, and the sutures also agree exactly with 
those of the old of that species. Comparing it with a specimen of Zurneri from 
Endigen of about the same size, it is seen that the latter has a much broader 
abdomen, deeper channels, more trenchant keel, and keeps its pile and form 
intact until a much later age, than Ast. acceleratum, and it does not increase in 
size so fast, is not so involute, and grows much larger. There are also several 
very fine specimens from Endigen, which enable us to connect acceleratum with 
stellare without the aid of the similar varieties from Semur or Gmiind, and they 
are regarded as so connected by Professor Fraas, who has labelled them Amm. 
obtusus. There is a series of five perfect specimens belonging to the Stuttgardt 
Museum, sufficient to convince the most sceptical. Nevertheless, it differs in the 
form of the young and in the adult from either s/ellare or obtusum, being both 
more involute and more accelerated in its mode of development. It is, as a rule, 
identified with Brook, and it bears the same relation to obluswm that Ast. ampendens 
bears to Turner. 
SECOND SUBSERIES. 
Asteroceras Turneri, Hyarr. 
Plate IX. Fig. 8,9. Summ. Pl. XIII. Fig. 3. 
Amm. Turneri, Sow., Min. Conch., V. p. 75, pl. cecclii. 
Aster. stellare, Hyarr, Bull. Mus. Comp. Zodl., I., No. V. p. 80. 
Amm. compressaries, Qumnst., Amm. Schwiib. Jura, p. 126, pl. xvii. fig. 4-6. 
Amm. cf. obtusus, QuENSsT., Ibid., p. 148, pl. xix. fig. 9. : 
Amm. undaries, Qumnst., Ibid., p. 148, pl. xx. fig. 2-6. 
Amm. Turneri, Quenst., Ibid., p. 142, pl. xix. fig. 5 (not fig, O-o). 
Arietites Turneri, Wricur, Lias Amm., p. 292, pl. xii. fig. 1-6, 
Localities. — Lyme Regis, Gloucester, Semur. 
The amount of involution on the third quarter of the sixth whorl is two fifths 
of the side. The abdomen is broader, the channels more deeply sunken and 
broader, and the keel thinner and less immature in its aspect, than in Ast. stellare 
or Ast. acceleratum. The sides also are flatter, and the dorsum is but very slightly 
broader than the abdomen. The umbilical shoulders are abrupt, but the umbili- 
cus is hardly so deep as in acceleratwm, the lateral increase of the shoulders by 
growth being considerably less than in that species, though greater than in typical 
varieties of oblusum. The pilse are thinner, more numerous, and do not have the 
? This figure is erroneous in one important particular. The youngest part of the abdomen visible 
in the figure, as seen from the front, is much flattened, whereas in the specimen it was but slightly more 
depressed than in the older part of the same whorl, represented as trigonal immediately below. 
