578 



MOLLUSCA 



SUB- KINGDOM VI 



(after Steinniai 



-lti/;, Miller sp. .Middle Dogger 

 and Doderlein). 



Lorraine 



only slightly confluent. Sonninia (JFaagenia, Bayle), (Fig. 1203); Witchellia, Buck- 

 man. Inferior Oolite. 



V. LlPAROCERATIDA. 



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- 

 flections 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 

 011 the venter of some forms, but form 

 very large continuous folds in others. 

 Sutures become excessively complex, 

 saddles narrow and deeply cut by com- 

 plex marginals, and ventral lobe corre- 

 sponds, but usually of about equal length with the lateral lobes. Aiitisiphoiial 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, Hyatt. 



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. 



Amblycoceras bifer. 



Tro-pidoceras (Harpoceras, Waagen), Platypleuroceras, Hyatt ; Acanthopleuroceras, 



nom. nov. Type A. (Amm.} natrix, Schloth. sp. [The latter name is substituted for 



Cycloceras, Hyatt, preoccupied among Nautiloids.] Middle Lias. 



VI. DACTYLIOIDA. 



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 



Middle Lias 



Dorsal sutures like those of 



