CLASö II BRACHIOPODA 375 



less open cleft during life, or only so in the youngest shelled stages, after 

 which the ventral valve may become cemented to foreign objects. Pedicle in 

 geologically younger forms often modified by a listrium. Homoeodeltidia and 

 pseudochilidia as a rule not well developed. 



Superfamily 1. SIPHONOTRETACEA Walcott and Schuchert. 



Primitive, thicJc-shelled, calcareous or corneous, obolid-like Neotremata, with the 

 pedicle passing through a ventral sheath, the aperture of which may remain apical 

 and circular in outline and posterior to the protegulum, or may become elongate 

 through resorption by passing anteriorly through the 'protegulum and umbo of the 

 shell. Ä listrium is not developed. Dorsal protegulum marginal. Cambrian to 

 Silurian. 



Family 1. Obolellidae Walcott and Schuchert. 



Primitive Siphonotretacea with the pedicle emerging through a small circular 

 Perforation in the apex of the ventral valve posterior to the protegulum. Derived out 

 of atrematous Biciinae. Cambrian. 



Obolella Billings (Fig. 552). Small, oval or round, thick shells resembling 

 Obolids but with a pedicle tube instead of an open furrow. Lower Cambrian 

 of North America and Sweden. The subgenus Glyptias Walcott, has trans- 

 verse parallel surface sculpturing. Lower Cambrian ; Sweden. 



i '^> : A- 



Fig. 552. 



Obolella atlantica Walcott. Lower 

 Cambrian ; Canada. A, Ventral valve ^ 

 showing vascular sinuses and fiUiug of „ re« 



pedicle foramen (/)). B, Side view of * '"• ^"'*- 



same. (', Dorsal interior showing the A-C, Sijihonotreta verrucosa Vern. Middle Ordovician ; 



striated cardinal area(a)and moulds of Esthonia. D, S. ungtdculataEichw., showing the internal 



the lateral scars (i) (after Walcott). opening of the pedicle aperture (after Walcott). 



Botsfordia Matthew (Mobergia Redlich). Like Obolella but with a highly 

 Ornate papillose surface. Cambrian ; North America. 



Schizopholis Waagen. Middle Cambrian of India. (?) Quebecia Walcott. 

 Lower Cambrian of eastern Canada. 



Family 2. Siphonotretidae Kiitorga. 



Progressive Siphonotretacea with the circular or elongate pedicle opening at the 

 apex or passing by resorption anteriorly through the protegulum aiul umbo of the 

 shell. Cambrian. 



Siphonotreta de Verneuil (Fig. 553). Large and elongate forms in. which 

 the pedicle sheath is long and well developed, external aperture small and 

 circular. External surface with hollow spines, though rarely preserved ; 

 shell substance punctured by radiating and branching tubules. Ordovician 

 und Silurian ; Europe and (?) North America. 



