236 
THE LIAS AMMONITES. 
compressed. Keel crenulated and well-defined. Umbilicus open, whorls exposed, or 
only partially involuted. Ex. AmaltJieus margaritatus, Mont. (PI. XLIX) ; the other 
forms named are all varieties of Montfort's capital typical species, 
CYCLOCERATIDiE. 
This family is remarkable for containing species which, on one side, ally it with 
LiPAROCERATiD^, and, on the other, with Hildoceratid.e. The form is more com- 
pressed than the former, and the tuberculations of the pilse separate it from the latter, 
Gemis Plattpleuroceras, Hyatt. — Abdomen nearly as broad, or broader than the 
dorsal side of the whorl. Pilse single, tuberculated, and extending across the rounded 
abdomen. Septa minutely divided by minor lobes. Ex. Aegoceras latecosta, Sow. 
(PI, XXXII, fig. 1). 
Genus Cycloceras, Hyatt. — Abdomen rounded or keeled, not so broad as the dorsal 
side of the whorl. Pil^ single, tuberculated, and not extending across the abdomen in 
the keeled species, young smooth for the first two or three whorls, then becoming ribbed, 
Ex. Aegoceras natrix, Schloth. Aegocer. Valdani, d'Orbig. (PL XXXVIII, figs. 1 — 4). 
Genus Tropidoceras, Hyatt. — Abdomen invariably keeled, much narrower than the 
dorsal side of the whorl. Pilse single, smooth, or tuberculaited in the same species, do 
not extend across the abdomen in any species. Young smooth for one or two whorls, 
keel and pilse appear simultaneously, Ex. Harjjoceras Masseanum, d'Orb. 
* 
Up])er Lias. 
Discoceratid^. 
OpJdoceras Levesquei, d'Orb. — Harpoceras Levesqiiei, d'Orb. 
Deroceratid^, 
Deroceras suharmatum, Sow, = Stephanoceras suharmatim. Sow, 
DACTYLOIDiE, 
Cceloceras Grenouillouxii, d'Orb, = Aegoceras pettos, Quenst. (PI. XXXVII, figs. 5 — 7). 
Genus Dactylioceras, Hyatt. — Abdomen equal in breadth, or less in width than 
the back, instead of being broader than, or equal in breadth to the back, as in the pre- 
ceding genera. The lateral pilse in the adult are smooth, and invariably single; the 
abdominal pilse may be either bifurcated or single. Ex. Steplianoceras commune, Sow, 
