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, Hyatt. 



Plate VIII. Fig. 4-8. Plate IX. Fig. 1. Suuim. PI. XIII. Fig. 8. 



Amm. obtusus, Sow., Min. Conch., II. p. 151, pi. clxvii. 



Amm. obtusus, D'Orb., Terr. Jurass. Ceph., p. 191, pi. xliv. 



Amm. obtusus, Quenst., Amm. Schwab. Jura, p. 141, pi. xix. fig. 2, 3. 



Ast. obtusus, Hyatt, Bull. Mus. Comp. Zodl., I., No. 5, p. 79. 



Ariel, obtusus, Wright, Lias Amm., p. 293, pi. xxi. fig. 1-5. 



Amm. Smithi, Sow., Min. Conch., IV. p. 148, pi. ccccvi. 



Amm. Smithi, Quenst., Amm. Schwab. Jura, p. 140, pi. xix. fig. 1. 



Amm. Turneri, Ziet., Verst. Wtirt., p. 15, pi. ii. fig. 5. 



Amm. Turneri, Quenst., Amm. Schwab. Jura, p. 143, pi. xix. fig. 10-13. 



Amm. stellaris, Hauer, Ceph. Lias Nordostl. Alpen, pi. v. fig. 1-3. 



AEgoc. sagittarium, Tate et Blake, Yorkshire Lias, pi. vii. fig. 2. 



yEgoc. sagittarium, Wright, Lias Amm., p. 355, pi. lii. fig. 1-5 ; pi. Ixii. A, fig. 1-6. 



<ffigoc. Slatteri, Wright, Lias Amm., p. 374, pl. 1. fig. 1-5 (not fig. 6-8). 



Amm. capricostatus, Quenst., Amm. Schwab. Jura, pl. xix. fig. 14, 15. 



Localities. — Lyme Regis, Whitby, Robin Hood's Bay, Boll, Balingen, Bempflingen, Salins, Besancon, 

 Ad net. 



Var. sagittarium. 



A specimen from Bempflingen has pike, which cross the abdomen. Speci- 

 mens in Quenstedt's collection from the same locality show this peculiar deforma- 

 tion, to which he calls attention, 1 and compares them with sagittarium, but does 

 not seem sure of the identification, since in another place (p. 252) he appears to 

 admit Wright's association of sagittarium with Jamesoni. 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 

 pilas with capricostatus, Quenst., and the Turneri deformation common in South 

 Germany, and their differences when compared narrowly with Jamesoni, leave 

 but little doubt that Wright was in error in thinking this form occurred in the 

 Jamesoni 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 Washneroceras, especially Wcehn. latimontanum, 2 is a remarkably 

 good example of morphological equivalence. 3 Others among these deformed 

 specimens, both in England and Germany, resemble Microceras 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 " St'amme 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. 



