CLASS II 



BRACHIOPODA 

 Late Ordovician to Devonian ; 



409 



North America and 



but continuous. 

 Europe. 



Glassia Davidson (Fig. G19). Small, smooth shells, with the apices of the 

 laterally compressed spirals situated at the centre of 

 the brachial cavity. Jugum similar to that of Atrypina. 

 Ordovician to Devonian ; Europe and America. 



Subfamily B. 



Atrypinae Waagen. 



Terminal Atrypidae with the jugum situated extremely 

 posteriorly, complete in young stages, hat at maturity dis- 

 continuous. Spiralia dorso-medially directed. Late Ordo- 

 vician to Devonian. 



Atrypa Dalman (Spirigerina d'Orb.) (Fig. 620). 

 Shell radially plicated, usually with lamellar expansions 

 or hollow spines. Spirals introverted, dorso-medially 

 directed. Jugum extremely posterior in position, and complete in young 



Pic. 619. 



Glassia obuvata (Sowerby). 

 Silurian ; Wenlock, England. 

 Interior of dorsal valve. '^/^ 

 (after Davidson). 



Fio. 620. 



Atry2^a reticularis (Liim.). Middle Devonian; Gerolstein. Eifel. ^1, Umlional aspect of adult specimen. B, 

 Ventral aspect and profile of youny shell. C, Interior of dorsal valve, showing spiralia, crura, and jugum. 

 D, Ventral valve, showing muscular and vascular impressions, a, Adductors ; c, Diductors ; (/, Deltidial plates ; 

 o, Ovaries ; p, Pedicle muscle. 



stages ; but mesially absorbed at maturity. Widely distributed in the late 

 Ordovician, Silurian and Devonian. 



Grueneivaldtia Tschernyschew. Atrypa-like shells, but with the relative 

 convexity of the valves reversed. Devonian ; Russia. 



(?) Karpinshya Tschernyschew. Elongate, Atryjpa-\\\iQ shells, with a median 

 dorsal septum. Devonian ; Russia. 



(1) Clintonella Hall and Clarke. Silurian ; North America. 



Subfamily C. 



Dayiinae Waagen. 



Fir;. 621. 



Dayia iiarirula(iiov/.). Silurian; Lud- 

 low, Shropshire, s/o (after Davidson). 



Derived Atrypidae with the jugum drawn out 

 posteriorly into a simple short process. Spiralia 

 laterally directed. 



Dayia Davidson (Fig. 621). Small smooth 

 shells, with the jugum situated anteriorly, and 

 drawn out posteriorly into a simple short process. 

 Spiralia laterally directed. Silurian ; Europe. 



