578 MOLLUSCA SUB-KINGDOM VI 
only slightly confluent. Sonninia (Waagenia, Bayle), (Fig. 1203); Witchellia, Buck- 
man. Inferior Oolite. 
V. LIPAROCERATIDA. 
Discoidal radical forms have more or 
less subquadrate volutions with coarse, 
fold-like, single, or bifurcated costae con- 
tinuous across the venter. External and 
dorsal sutures limited in number of in- 
Jlections as in Arietidae, but development 
of marginals carried to utmost degree of 
complexity in this sub-order. Keel solid 
when present. Two rows of large nodes 
or spines sometimes developed on either 
side. 
Family 11. Liparoceratidae. 
Volutions remain rounded in section and 
frequently retain a primitive discoidal 
aspect. Costae almost entirely disappear 
on the venter of some forms, but form 
very large continuous folds in others. 
Bic. 1203. Sutures become excessively complex, 
ceytgade Sawer aes op, Middle Dossers Loraine saddles narrow and deeply eut by com. 
plex marginals, and ventral lobe corre- 
sponds, but usually of about equal length with the lateral lobes. Antisiphonal bifid, 
and resembles (as do also the two 
dorsal saddles and small dorsal lobes) 
those of Arietidae. 
Liparoceras, Microderoceras, Am- 
blycoceras (Microceras), Hyatt (Fig. 
1204); Androgynoceras, Hyat t. 
Lower and Middle Lias. 
Family 12. Tropidoceratidae. 
Discoidal compressed shells with 
straight costae that cross the venter 
in some forms approximating to Am- 
blycoceras, but usually this region is 
distinctly elevated, and smooth or 
keeled along the median zone. Costae 
have two rows of tubercles in several 
species, but may be smooth in others. 
Sutures similar to those of Uptonia, 
but more complex; lobes, however, 
exceedingly narrow and auxiliary line inclined apicad. Dorsal sutures like those of 
Amblycoceras bifer. 
Tropidoceras (Harpoceras, Waagen), Platyplewroceras, Hyatt ; Acanthoplewroceras, 
nom. nov. Type A. (Amm.) natriz, Schloth. sp. [The latter name is substituted for 
Cycloceras, Hyatt, preoccupied among Nautiloids.} Middle Lias. 


Fic. 1204. 
Amblycoceras capricornus, Schloth. sp. Middle Lias; 
Gmuind, Wiirtemberg. 
VI. Dactynrorpa, 
Young have volutions with trapezoidal sections, venter broader than dorsum and 
decidedly coronate, or with a line of nodes along the ventro-lateral angles, and broad 
