CLASS II 



BRACHIOPODA 



417 



few plications, crossed by fine, often imbricating growth lines. Jugum 

 originating near the mid-length of the primary lamellae, uniting and forming 

 a simple upright stem articulating in a cavity in the ventral valve. Dorsal 

 valve with a high median septum. Devonian ; Germany and France. 



Coelospira Hall. Shells externally much like Atrypina, but with laterally 

 directed spirals. Jugum similar to that of Anoplotheca. Silurian and 

 Devonian ; America and Europe. Subgenus : Leptocoelia Hall. Larger shells 

 with coarser plications. Silurian and Devonian ; widely distributed. 



Anabaia Clarke. Similar to Coelospira, but with a highly convex dorsal 

 valve. Silurian ; Brazil and North America. 



Vitulina Hall. Like Coelospira, bv;t with few plications and a long 

 hinge-line. Plications covered with fine radiating lines or rows of pustules. 

 Devonian ; America and South Africa. 



Family 9. Athyridae Phillips. 



Specialised Spiriferacea, with the bases of the primary lamellae situated between 

 the spiralia and sharply recurved dorsally at their junction with the crura. Spiralia 

 laterally directed. Jugum complete, V-shaped, with the apex drawn out into a simple 

 process which bifurcates ; this elongates and enters more or less extensively between the 

 lamellae of the spiralia. Shells smooth, lamellose, or spinose ; structure impunctate. 

 Devonian to Triassic. 



Subfamily A. Athyrinae Waagen. 



Primitive Athyridae, in which the single process of the jugum bifurcates. The 

 branches usually terminate between the first and second volutions of the spiralia. 

 Shells lamellose or spinose. 



Fio. 632. 



Athyris concentrica (von Bnch). A, Shell with dorsal valve partly removed. B, Interior of dorsal valve, 

 i/i- C, D, Frontal and lateral aspect of spiralia (after Davidson). 



Athyris M'Coy {Cleiothyris Phillips, non King ; Spirigera d'Orb. ; Euihyris 

 Quenstedt) (Fig. 632). 



Sub-equally biconvex shells with concentric growth lines extended into 

 lamellae. Ventral umbo not prominent, incurved, usually concealing the 

 pedicle opening and deltidial plates. Teeth supi:)orted by dental lamellae. 

 Hinge-plate of the dorsal valve perforated by a "visceral foramen." The 

 peculiar jugum of this genus is illustrated in Fig. 632, C, D. Devonian and 

 Carboniferous ; distribution general. 



Anathyris von Peetz. Athyrids with straight hinge-lines and a hidden 

 ventral area. Devonian ; Europe. 



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