334 MOLLUSCOIDEA—BRACHIOPODA SUB-KINGDOM V 
with the complete jugum decidedly posterior in position. Ordovician and 
Silurian ; North America. 
Atrypina, Hall and Clarke. Primitive dfrypae with few plications, and 
but three or four volutions in each spiral. Jugum as in Afrypa, but continuous. 
Silurian to Devonian ; 
North America and 
Europe. 
Glassia, Davidson 
(Fig. 570). Small smooth 
shells, with the apices of 
the laterally compressed 
spirals situated at the 
centre of the brachial 

Fic. 570. Rene cavity. Jugum similar 
Glassia obovata, Sow. sp. “ : : “UNIN oe 
Silurian ; Wenlock, England. Dayia navicula, Sow. sp. Silurian ; to that of Atrypina. Or 
Interior of dorsal valve, 3/; Ludlow, Shropshire. 4/2 (after David- dovician to Devonian 
(after Davidson). son). ¢ 
Europe. 
Dayia, Davidson (Fig. 571). Small smooth shells, with the jugum situated 
anteriorly, and drawn out posteriorly into a simple short process. Spiralia 
laterally directed. Silurian ; Europe. 
Atrypa, Dalman (Cleiothyris, Phill. ; Spirigerina, @Orb.), (Fig. 572). Shell 
radially plicated, usually with lamellar expansions or hollow spines. Spirals 
introverted, dorso-medially directed. Jugum extremely posterior in position, 

Atrypa reticularis, Lin. sp. Middle Devonian; Gerolstein, Hifel. A, Dorsal aspect of adult specimen. 
B, Ventral aspect and profile of young shell. C, Interior of dorsal valve, showing spiralia, crura, and jugum. 
D, Ventral valve, showing muscular and vascular impressions (a, Adductors ; c, Diductors ; d, Deltidial plates ; 
0, Ovaries ; p, Pedicle muscle). 
and complete in young stages; but mesially absorbed at maturity. Widely 
distributed in the Silurian and Devonian. 
Gruenewaldtia, Tschernyschew. <Atrypa-like shells, but with the relative 
convexity of the valves reversed. Devonian; Russia. 
? Karpinskya, Tschernyschew. Elongate, dtrypa-like shells, with a median 
dorsal septum. Devonian; Russia. 
? Clintonella, Hall and Clarke. Silurian; North America. 
Family 2. Spiriferidae. King. 
Spiriferacea with the crura directly continuous with the bases of the primary 
lamellae, which are situated between the laterally directed spiralia. Jugum simple, 
complete, or incomplete. Silurian to Jurassic. 
