CLASS II 



BRACHIOPODA 



373 



Siilafamily D. Biciinae Walcott and Schuchert. 



Progressive OhoUdae with the pedicle restricted to the ventral valve and more or 

 less enclosed by a pedicle tube. Articulation rudimentary. Out of this stock have 

 arisen the Obolellidae of the Neotremata. Cambrian. 



Bicia Walcott. Lower Cambrian of Quebec and New York. 

 Hall. Middle Cambrian of North America. 



Dicellomus 



Family 3. Trimerellidae Davidson and King. 



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

 very prominent, triangular and transversely striated. Adjustor and anterior adductor 

 muscles 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 Dall) (Fig. 549). Platforms long, narrow, 



Fig. 549. 



Trimerella llndstroemi (Dall). Silurian ; Gotland, 1/2. A, 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 

 Lindstrijm.) 



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 Faroe. 

 Ehinobolus Hall. Silurian ; North America. 



Superfamily 4. LINGULACEA Waagen. 



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

 with a more or less long, worm-like, tubular, flexible pedicle. Ordovician to Recent. 



Family 1. Lingulidae Gray. 



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

 or less long, tubular, flexible pedicle. Muscles highly differentiated and consisting of 



