Hyatt.} 12 [January 17, 
CYCLOCERAS. 
Cycloceras natrix. 
Amm. natrix Schlot. Petrefact. 
Amm. natriz Ziet. Verst. Wurt., p. 5, pl. 4, fig. 5. 
Cycloceras natrix Hyatt, Bull. Mus. Comp. Zoology, no. v, p. 92. 
The adult alone was observed, and only fragments of the whorl, 
but these showed two lines of tubercles, single pile not stretching — 
across the abdomen, the latter region elevated and keeled. Amm. 
natriz Ziet., according to Oppel, is the same as Amm. brevispina Sow., 
but the figure of the former has a distinct keel, whereas the latter 
has none. 
Cycloceras bipunctatus. 
Amm. bipunctatus Roem., Ool. p. 193. 
Amm. Valdani D’Orb., Terr. Jurass., Ceph., p. 255, pl. 71 
Amm. compressus Quenstedt, Die Ceph., p. 90, pl. 5, fig. 3 
Amin. Valdani Quenstedt, der Jura., p. 131, pl. 16, figs. 2, 3. 
Cycloceras Valdani Hyatt, Bull. Mus. Comp. Zoology, no. v, p. 95. 
Amm. bipunctatus Oppel, der Jura., p. 280. 
The young of this species shows at an early age the keel and flat- 
tened whorl of the adult, thus showing no material difference either 
in development or adult characteristics from -Tropidoceras, which 
genus is therefore suppressed. 
Cycloceras Actzeon. 
Amm. Acteon D’Orb., Terr. Jurass., Ceph., p. 232, pil 61, figs. 1-3. 
Tropidoceras Acton Hyatt, Bull. Mus. Comp. Zoology, no. v, p. 93. 
This species is very closely allied to Cycloceras bipunctatum, and I 
much doubt the propriety of separating the two. The material at 
my command, however, does not permit me to examine the younger 
stages of Cycloceras Valdani, with the requisite fullness and accuracy. 
Cycloceras Aigegeon. 
Amm. Aigeon D’Orb., Terr. Jurass., Ceph., p. 2384, pl. 61, figs. 4-6. 
Tropidoceras Aigeon Hyatt, Bull. Mus. Comp. Ziooleeet no. V, 
Pp: 93. 
The progressive flattening of the sides and elevation of the abdo- 
men reach a very advanced stage in this species. 
Cycloceras Masseanum. 
Amm. Masseanus D’Orb., Terr. Jurass., Ceph., p. 225, pl. 58. 
Amm. Masseanus Quenstedt, Die Ceph., p. 90, pl. 5, fig. 2. 
Tropidoceras Masseanum Hyatt, Bull. Mus. Comp. Zoclogy, no. v, 
p. 93. 
