FIFTH, OR AGASSICERAN BRANCH. 201 
convergent, more involute, and smoother, and the sutures more degenerate, but 
the keel, so far as observed, though it may become much depressed, never wholly 
disappears. Probably this does occur in extremely aged specimens, in what we 
have called the nostologic stage, but such extreme examples have not yet been 
seen by the author. 
First SuBSERIES. 
Asteroceras obtusum, Hyarr. 
Plate VIII. Fig. 4-8. Plate IX. Fig. 1. Summ. Pl. XIII. Fig. 2. 
Amm. obtusus, Sow., Min. Conch., II. p. 151, pl. elxvii. 
Amm. obtusus, D’Orp., Terr. Jurass. Ceph., p. 191, pl. xliv. 
Amm. obtusus, Quenst., Amm, Schwiib. Jura, p. 141, pl. xix. fig. 2, 3. 
Ast. obtusus, Hyatt, Bull. Mus. Comp. Zodl., I., No. 4, p. 79. 
Ariet. obtusus, Wricut, Lias Amm., p. 293, pl. xxi. fig. 1-5. 
Amm. Smithi, Sow., Min. Conch., IV. p. 148, pl. eccevi. 
Amm. Smithi, Quenst., Amm. Schwib. Jura, p. 140, pl. xix. fig. 1. 
Amm. Turneri, Z1eT., Verst. Wiirt., p. 15, pl. ii. fig. 5. 
Amm. Turneri, Quenst., Amm. Schwib. Jura, p. 143, pl. xix. fig. 10-13. 
Amm. stellaris, HavER, Ceph. Lias Nordéstl. Alpen, pl. v. fig. 1-3. 
Aigoc. sagittarium, Tare et Buaxn, Yorkshire Lias, pl. vii. fig. 2. 
Aigoc. sagittarium, Wrient, Lias Amm., p. 355, pl. lii. fig. 1-5 ; pl. Isii. a, fig. 1-6. 
4igoc. Slatteri, Wriaut, Lias Amm,, p. 374, pl. 1. fig. 1-5 (not fig. 6-8). 
Amm. capricostatus, QuENST., Amm. Schwiib. Jura, pl. xix. fig. 14, 15. 
Localities. —Lyme Regis, Whitby, Robin Hood’s Bay, Boll, Balingen, Bempflingen, Salins, Besancon, 
Adnet. 
Var. sagittarium. 
A specimen from Bempflingen has pile, which cross the abdomen. Speci- 
mens in Quenstedt’s collection from the same locality show this peculiar deforma- 
tion, to which he calls attention,’ and compares them with sagitlarium, but does 
not seem sure of the identification, since in another place (p. 252) he appears to 
admit Wright’s association of sagittarium with Jumesoni. Blake states that his 
types came from the lower part of the Oxynotus bed, that is, from the Obtusus 
bed of other authors. This fact, and the obvious agreement of the sutures and 
piles with capricostatus, Quenst., and the Turneri deformation common in South 
Germany, and their differences when compared narrowly with Jameson, leave 
but little doubt that Wright was in error in thinking this form occurred in the 
Jameson’ bed, or was identical with Jamesoni. The specimens figured represent 
quite completely what is perhaps the most remarkable degradational series of 
the Lias. The resemblance of one of Wright’s figures, Plate LIT. Fig. 1, 2, to 
the forms of Wehneroceras, especially Wehn. latimontanum,? is a remarkably 
good example of morphological equivalence.’ Others among these deformed 
specimens, both in England and Germany, resemble AMicroceras planicosta in the 
1 Amm. Schwab. Jura, p. 145, 
2 Unter. Lias, Mojsis. et Neum., Beitr., II. pl. xx. 
8 A very remarkable example of morphological equivalence caused by a wound is figured by Neumayr 
in his ‘‘ Stiimme des Thierreichs,’’/1889, p. 82. The shell of a keeled and channelled species has been 
broken on the abdomen, and beyond the wound the characteristics have changed so as to resemble those of 
Schlotheimia. 
26 
