FIFTH, OR AGASSICERAN BRANCH. Zit 
Asteroceras impendens, Hyarr. 
Plate X. Fig. 6-9. 
Ariet, impendens, Wricut, Lias Amm., p. 302, pl. xxii. a, fig. 1-5. 
Ariet. Collenoti, Ibid., p. 304, pl. xxii. a, fig. 6~9; pl. xxii. x, fig. 1-3. 
Amm. Fowleri, Buckm., Murch. Geol. Cheltenh., pl xii fis. 7: 
Amm. impendens, Quenst., Amm.:Schwib. Jura, p. 151, pl. xx. fig. 7-10. 
Ariet. impendens, BLaxe, Yorkshire Lias, pl. vi. fig. 7. 
Localities. — Semur, Lyme Regis. 
This species differs from Brooki in the greater amount of the involution, the 
smaller size, the earlier age at which the same form of whorl is passed through, 
and the earlier age at which degeneration begins. 
In Wright’s “ Lias Ammonites” the figures of Brookt, impendens, and Collenoti 
show in the clearest manner what are the proper limits of the species. The fig- 
ure of Brooki, on Plate VI. Fig. 4, is taken from the less involute form, which 
retains its pile until a late stage of growth; that of Collenoti on Plate XXII. B 
is an old and very large individual of impendens, which approximates to Brooki, but 
has the usual difference in the amount of involution and begins to show degen- 
eration of the pilx also earlier than is common in Brooki,; that of Collenoti on 
Plate XXII. A, Fig. 6-8, is a yet more accelerated form, growing old and losing 
pile, etc. earlier than in the specimen shown on Plate XXII B. The figure of 
impendens itself is still more accelerated than the specimen figured on Plate 
XXII. A, Fig. 6-8, and has also somewhat stouter whorls. The young figured 
on Plate XXII. A, Fig. 4, is similar to the adult of the true Ast. Brooki, having 
the same form, pile, and involution until a late nealogic stage. 
All of these forms have the broad abdomen, the peculiar channels, and the 
young like Brooki, and are quite distinct from the true As¢. Collenoti. They are 
undoubtedly transitional forms connecting the two species. Those who wish may 
join them, but, as we have previously said, all the series and about all the species 
of the Arietidx are closely connected by intermediate forms and modifications, 
and, to be really consistent, we must then also include the entire family under 
a single specific name. We doubt if any paleontologist would secure serious 
support if he attempted to do this. 
Asteroceras denotatum, Hyarr. 
Amm. denotaius, Srmps., Foss. Yorkshire Lias, p. 76. 
Ariet. denotatus, Wrieut, Lias Amm., pl. vi. fig. 1 (Collenots in the text, p. 804). 
Amm. tenellus, Simps., Foss. Yorkshire Lias, p. 97? 
This species has been universally placed either with Brooki or Collenoti. It is, 
however, quite distinct from either of these forms. If one compares the figure 
of denotatus by Wright with the young of impendens figured by the same author on 
Plate XXII. A, Fig. 4, and that of the young of the same species by Quenstedt, 
Amm. Schwiib. Jura, Plate XX. Fig. 8, it will be seen that denotatus stands just 
between tmpendens and Collenoti. The young of impendens is much less involute, 
and shows the same stout whorl as in the adult, a form which is in strong con- 
