234 
THE LIAS AMMONITES. 
pilae in tlie adult are undivided on the abdomen, and continuous with the large, single 
lateral pilae, which last may be ornamented with one or two rows of small tubercles, or 
may be bare. Ex. Aegoceras polymorphum, Quenst. (PI. XL, fig. 1). 
Deroceratid^. 
Genus Deroceras, Hyatt. — Whorl circular; pilae depressed; linear between, and 
bifurcated on the tubercles. Tubercles large, prominent, pointed, and in a single row. 
Ex. Aegoceras planicosta, Sow. (PI. XXIV). 
Middle Lias. 
LlPAROCERATID^. 
Genus Microceras, Hyatt. — Ex. Microceras planicosta = Aeyoceras planicosta, Sow. 
(PI, XXIV) ; Microceras maculatum. Young and V>\x^=. Aegoceras capricornus, Schloth. 
Genus Androgynoceras, Hyatt. — The sides of the adult whorl slope outward and 
are ornamented with pilae, usually single, and set two rows of tubercles. Abdomen 
narrow. The large pilae of the young are split into smaller pilae on the abdomen of the 
adult, but usually retain the characters of Microceras until a late period of growth. 
Ex. Aegoceras heterogenum, Young and Bird — ^6^^. hybridimi, d'Orb. (PL XXXVI). 
Genus Liparoceras, Hyatt. — This genus differs from both of those previously 
described in the greater breadth of the abdomen, the greater increase of the radii of the 
spiral, consequently smaller number of whorls and the larger size of the species. Ex. 
Aegoceras Henleyi ■= Aeg. striatum, Reinecke; Aeg. Bechei, Sow. (PI. XXXIII). 
Deroceratid/E. 
Genus Deroceras, Hyatt. — Ex. Deroceras Davoei— Aeg. Davcei, Sow. (PI. XXXI, 
fig. I); Deroceras densinodum^=^ Aegoceras densinodum, Quenst. (PI. XXXVIII, fig. 5); 
Deroceras armatum— Aegoceras armatum, Sow. (PI. XXVIII, fig. 1). 
Genus Peronoceras, Hyatt. — Abdomen depressed ; pilae flattened ; linear between 
the tubercles ; usually but not invariably bifurcated by the tubercles on the sides, though 
invariably bifurcated on the abdomen. Ex. Stepkanoceras jihulatum, Sow., and Steph. 
mharmatum, Sow. ; both are Upper-Lias species. 
Thysanoidji;. 
This family includes the Eimbriati, Ligati, and Heterophylli, which agree in the 
foliaceous character of the septa. 
