CLASS II 



BRACHIOPODA 



409 



but contiriuous. Late Ordovician to Devonian ; North America and 

 Euroj^e. 



Glassia Davidson (Fig. 619). 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, but at maturity dis- 

 continuous. Spiralia dorso-medially directed, Late Ordo- 

 vician to Devonian. 



Atrypa Dalman {Spirigerina d'Orb.) (Fig. 620). sifuS"; WeÄÄS: 

 Shell radially plicated, usually with lamellar expansions J"^'^"'g of dorsal vaive. s/^ 

 or hollow spines. Spirals introverted, dorso-medially 

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



Fio, 619. 



Fig. 620. 



Atrypa reticularis (Linn.). Middle Devonian; Gerolstein. Eifel. ^, Umbonal aspect of adultspecimen. B, 

 Ventral aspect and profile of young shell. C, Interior of dorsal valve, showing spiralia, crnra, and jugum. 

 D, Ventral valve, showing muscular and vascular impressions. a, Adductors ; c, Diductors ; d, 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, Atrypa-like shells, with a median 

 dorsal septum. Devonian ; Russia. 



(?) Glintonella Hall and Clarke. Silurian ; North America. 



Fio. 621. 



Daiiianavicitla (ßow.). Silurian; Lud- 

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



Subfamily C. Dayiinae Waagen. 



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. 



