CLASft II BRACHIOPODA 373 



Subfamily D. Biciinae Walcott and Schuchert. 



Progressive Obolidae with the pedicle restrided to the ventral valve and more or 

 less endosed by a pedide tuhe. Articulation rudimentary. Out of ihis stock have 

 arisen the Oholellidae of the Neotremata. Cambrian. 



Bida Walcott. Lower Cambrian of Quebec and New York. Dicellomus 

 Hall. Middle Cambrian of North America. 



Family 3. Trimerellidae Davidson and King. 



Large, thick-shelled, inequivalved Obolacea, with the ventral cardinal area usually 

 very prominent, triangulär and transversely striated. Adjnstor and anterior addudor 

 musdes elevated upon solid or excavated platforms. Ordovician and Silurian. 



Dinobolus Hall (Conradia Hall ; Obolellina Billings). Cardinal area not so 

 prominent as in the other genera of this family. Platform small, with abruptly 

 conical vaults. Ordovician and Silurian ; North America, Great Britain, 

 Bohemia, Gotland and Esthonia. 



Monomerella Billings. Similar to Trimerella, with well-developed platforms 

 in both valves ; that of the dorsal valve, however, but slightly excavated. 

 Silurian ; North America, Gotland and Livonia. 



Trimerella Billings (Gotlandia Dali) (Fig. 549). Platforms long, narrow. 



Fio. 549. 

 TriTnerella Undstroemi (Dali). Silurian ; Gotland, 1/2- ^. Shell seen from the dorsal side. B, C, Interior 

 of dorsal and ventral valves respectively. D, Internal mould. (A and B after Davidson ; C and D after 



Lind ström,) 



well developed and doubly vaulted. Dorsal beak often thickened into a 

 prominent apophysis extending against the cardinal slope of the ventral valve. 

 Silurian ; North America, Gotland and Faröe. 

 Bhinobolus Hall. Silurian ; North America. 



Superfamily 4. LINGULACEA Waagen. 



Elongate, thin-shelled, corneous, burrowing Atremata, derived out of Obolinue, 

 with a more or less long, worm-like, tubulär, flexible pedide. Ordovician to Recent. 



Family 1. Lingulidae Gray. 



Attenuate, sub-quadrate or spatulate, almost equivalved Lingulacea, with a more 

 or less long, tubulär, flexible pedide. Musdes highly differentiated and consisting of 



