BRACHIOPODA. 



373 



a broad 4-partite hinge-plate, mth processes from tlie outer 

 angles of the dental sockets ; crura of the spires united hy a 

 transverse band supporting a small process. Fossil, 2 species. 

 Upper Lias, Normandy. 



ATBrmis, M'Coy. 



Etymology, a, without, thuris, a door* (i.e. deltidium). 



Synonyms, Spirigera, D'Orbigny. Cleiothyris, King (not 

 Phil.). 



Types, A. concentrica, Buch. A. Eoissyi, Figs. 169, 170. 

 A. lamellosa, PI. XV., Fig. 16. 



Shell impunctate, transyersely oval, or sub -orbicular, bi- 

 convex, smooth, or ornamented with squamose lines of growth, 

 sometimes developed into wing-like expansions (Fig. iTOf); 



Fiff. 169. Interior of dorsal valve. 



Fig. 170. Specimen with fringe. 



hinge-line curved, area obsolete, foramen round, truncating the 

 beak, deltidium obsolete ; hinge-plate of dorsal valve with four 

 muscular cavities, i^erforated by a small round foramen, and 

 supporting a small complicated loop (?) between the spires; 

 spires directed outwards, crura united by a prominent oral 

 loop. 



The foramen in the hinge- plate occupies the situation of the 

 notch through which the intestine passes in the recent Rhyn- 

 cJionelke ; in A. concentrica a slender curved tube is sometimes 

 attached to the foramen, beneath the hinge -plate. A. tumida 

 has the hinge-plate merely grooved, and the byssal foramen is 

 angular. 



Fossil, about 70 species. Silurian — Lias. North and South 

 America and Eui'ope. 



* Sometimes employed, incorrectly, in the sense of a ^oor-way or for men. 

 t The spurious genus Actinoconchus (M'Coy) was founded on this character ; simi?at 

 expansions are formed by species of Atrypa, Camarophoria, and Producta, 



