BHACHIOPODA. 



389 



Crania; and three pair of adjuster muscles for keeping the 

 valves opposed to each other. Some of these are probably 

 inserted in the pedicle. The oral cirri are extremely tender and 

 flexible, contrasting with th^ stiflf and brittle setse of the mantle, 



Dorsal. Fig. 198. Ventral lobe. 



Discina lamellosa, Brod, ^ 

 w, umbo ; /, foramen ; d, disk ; a, anterior adductors ; a', posterior adductors ; 

 e, c', central and posterior adjustors ; r, external adjusters. The martle-fringe is not 

 represented in Fig. 198. 



which are themselves setose like the bristles of certain annelides 

 {e.g the sea-mouse, Aphrodite). The relation of the animal to 

 the perforate and imperforate valves is shown to be the same as 

 in Terehratida, by the labial fringe ; but the only process which 

 can possihly have afforded support to the oral arms is developed 

 from the centre of the ventral valve, as in Crania. Baron 

 Eyckholt has represented a Devonian fossil from Belgium, with 

 a fringed border; but if this shell is the Crania obsoleta of 

 Groldfuss, the fringe must belong to the shell, and not to the 

 mantle. 



Distribution, 10 species. West Africa, Malacca, Peru, and 

 Panama. 



Fossil, 64 species. Silurian-r— . Europe, United States, 

 Falkland Islands. 



In some species the valves are equally convex, and the 

 foramen occupies the end of a narrow groove. 



Sub-genus. Trematis, Sharpe. (=Orbicella, D'Orbigny.) 

 T. terminalis, Emmons. Yalves convex, superficially punctate; 

 dorsal valve with a thickened hinge-margin (and three diverg- 

 ing plates, indicated on casts. — Sharpe). Fossil, 14 species, 

 Lower and Upper Silurian. North America and Europe. 



