234 THE LIAS AMMONITES. 



pilse in the adult are undivided on the abdomen, and continuous with the large, single 

 lateral pilse, which last may be ornamented with one or two rows of small tubercles, or 

 may be bare. Ex. Aegoceras jpolymovphum, Quenst. (PL XL, fig. 1). 



DEROCEEATIDiE. 



Genus Derooeras, Hyatt. — Whorl circular; pilse depressed; linear between, and 

 bifurcated on the tubercles. Tubercles large, prominent, pointed, and in a single row. 

 Ex. Aeyoceras planicosta. Sow. (PI. XXIV). 



Middle Lias. 



LlPAROCERATID^. 



Genus Microceras, Hyatt. — Ex. Microceras planicosta = Aegoceras planicosta. Sow. 

 (PI, XXIV) ; Microceras maculatum, Young and Bird = Aegoceras capricornus, Schloth. 



Genus Androgynoceras, Hyatt. — The sides of the adult whorl slope outward and 

 are ornamented with pilse, usually single, and set with two rows of tubercles. Abdomen 

 narroM^ The large pilse of the young are split into smaller pilse 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 = ^e^. hybridum, 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. Becliei, Sow. (PL XXXIII). 



DEROCERA'L'IDiE. 



Genus Deroceras, Hyatt. — Ex. Deroceras Davmi=^ Aeg. Davmi, Sow, (PL XXXI, 

 fig. 1); Deroceras densinodum^ Aegoceras densinoduvi, Quenst. (PL XXXVIII, fig. 5); 

 Deroceras armatum = Aegoceras armatum, Sow. (PL XXVIII, fig. 1). 



Genus Peronoceras, Hyatt. — Abdomen depressed ; pilse flattened ; Hnear between 

 the tubercles ; usually but not invariably bifurcated by the tubercles on the sides, though 

 invariably bifurcated on the abdomen. Ex. Stephanoceras Jibulatum, Sow., and Steph. 

 subarmatum, Sow. ; both are Upper-Lias species. 



ThTSANOIDJ;!. 



This family includes the E'imbriati, Ligati, and Heterophylli, which agree in the 

 foliaceous character of the septa. 



