BEACmorODA. 



385 



edges rolled together and imited, forming a large permanently 

 open tube for the brachial currents. The large spines are most 

 usually situated on the ears of the ventral valve, and may have 

 served to moor the shell ; being tubular they were permanently 

 susceptible of growth and repair. Although edentulous, the 

 dorsal valve must have turned on its long hinge-line with as 

 much precision as in those genera which are regularly articulated 

 by teeth. 



Fossil, 81 species. Devonian — Permian. North and South 

 America, Europe, Spitzbergen, Thibet, Australia. 



Exterior. 



Fi?. 100. 



Interior. 



Suh-genus. ^wZosie^res, Helmersen. A. Wangenheimii, Yern., 

 Fig. 190. Permian, Eusssia; Carb. Shell like Producta; 

 ventral valve with a large flat triangular hinge-area (A), with a 

 narrow convex pseudo-deltidium [d] in the centre ; beak a little 

 distorted, as if attached when young ; dorsal valve slightly 

 convex near the umbo ; interior as in Productus {lungi-spinus). 



Steophalosia, King. 



Example, S. Cancrini, De Yern., Fig. 

 101. 



Synonym, Orthothrix, Geinitz. 



Shell attached by the umbo of the 

 ventral valve ; sub-quadrate ; covered 

 with long slender spines ; valves arti- 

 culated, dorsal moderately concave, 

 ventral convex, each with a small area ; 

 fissure covered; vascular impressions 

 conjoined, reniform. 



Fossil, 8 species. Devonian — Carb. 

 Europe, Himalaya (Gerard). 



101. ^. C>uicr:ni. 



