408 



MOLLUSCOIDEA 



PHYLÜM V 



Magellania Bayle {Wa 



Terehratella d'Orb. {Delthyris Menke ; Ismenia King ; Waltonia Davidson) 

 (Fig. 616). Jura to Recent. 



King; Neothyris Douville) (Figs. 534, 535, 



617). Jura to Recent. 



Bhynchorma (Ehlert. Cre- 

 taceous. Megerlina Deslong- 

 champs. Recent. Kraussina 

 Davidson (Kraussia Davidson, 

 non Dana 1852). Recent. 

 Mannia Dewalque. Miocene. 

 (?) Bhynchora Dalman. Cretace- 

 ous. 



Superfamily 3. 

 SPIRIFERACEA Waagen. 



Telotremata with the adult 

 j^^ brachia supported hy calcareous 



Fig. 616. 



Terehratella dorsata 

 (Lam.). Recent; Chili. 



lA. 



Fig. 61^ 



Magellania flavescens (Val.). ^.„ . . 7 . r^ 



Cent ;■ Australia. Interior of dorsal Spiral lamellae OT Spiralia. Or- 

 valve, somewhat enlarsed. j • • j. t 



dovician to Jurassic. 



The Spiriferacea are abundantly represented from the Silurian tö the Carboni- 

 ferous, during which time the jugum undergoes many and often rapid changes. The 

 brach idia in Zygospira are known to begin with a Gentronella-like loop, as in the 

 primitive Terebratulacea. 



Family 1. Atrypidae Gill. 



Divergent Spiriferacea with the crura directly continuous with the primary 

 lamellae, which diverge widely and have the spiral cones hetween them. Jugum 

 simple, complete, or incomplete. Ordovician to Devonian. 



Subfamily A. Zygospirinae Waagen. 



Primitive Atrypidae with a simple jugum, either posteriorly or anteriorly 

 directed. Spiralia with apices directed tovjard the median dorsal region. Ordovician 

 to Devonian. 



Zygospira Hall (Anazyga Davidson ; Orthonomaea 

 and Schuchert ; Protozyga Hall and Clarke) (Fig. 

 618). Like Atrypa, but small, and the spirals 

 composed of fewer coils. Jugum a simple con- 

 necting band, situated rather anteriorly. Sur- 

 face sharply plicate, never lamellose. Ordovician 

 and Silurian ; North America. 



Catazyga Hall and Clarke. More rotund and 

 finely striated than Zygospira, with the complete 

 jugum decidedly posterior in position. Ordo- 

 vician and Silurian ; North America. 



Atrypina Hall and Clarke. Primitive Atrypae 

 with few plications, and but three or four 

 volutions in each spiral. Jugum as in Atrypa, 



Hall : Hallina Winchell 



Fig. 618. 



Zygospira modeffta Hall. Ordovician 

 Cincinnati, Ohio. «Vi (after Hall). 



