374 



MOLLUSCOIDEA 



PHYLtTM V 



six pairs, two of adductors, and four of sliders or adjustors. Ordovician to 

 Recent. Maximum development in Ordovician, declining after Devonian time. 



a 



pair 



of 



Pseudolingula Mickwitz. Has a ventral pedicle groove and 

 umbonal muscles. Ordovician and Silurian ; Europe and America. 



Lingula Bruguiere (P/iare^ra Bolton ; Lingularius Dumeril); {snhgen. Glossina 



Phill.) (Figs. 550, 551). Shell thin, usually 

 compressed, glistening, generally smooth, or 

 with fine, concentric, more rarely with both 

 concentric and radial striae ; broad over the 

 pallial region, tapering more or less toward the 

 beaks. Ordovician to Recent. Maximum 

 development in Silurian and Devonian. 



Glottidia Dall. Like the preceding, but 

 interior of ventral valve with two septal ridges 

 diverging from the beaks. Dorsal valve with 

 a single median ridge. Recent; American seas. 

 Dignomia Hall. Both valves with median 

 seplal ridges ; that of the 

 \'\ dorsal valve stronger, and 

 flanked by two submarginal 

 diverging ridges, which cor- 

 respond in position to grooves 

 in the ventral valve. Middle 

 Devonian ; North America. 

 BarroiseUa Hall and Clarke. 

 Lingulids with rudimentary articulation. Silurian and Devonian ; North 

 America ; (?) Bohemia. 



Thomasina Hall and Clarke. Lingulids with the posterior margin of the 

 ventral valve notched, and with two conspicuous articulating processes. 

 Silurian ; France. 



Lingulipora Girty. 



Linijula anatina Brug. Recent. A, Shell 

 with pedicle. B, Interior of ventral valve. 



Fi(i. 5.Jl. 



Lingula lewisii Sow. 

 Silurian ; Gotland. 



Lower Carboniferous ; North America. 



Lingulids with a punctate shell. Devonian and 



Family 2. Lingulasmatidae Wincliell and Scliuchert. 



Platform-hearing Lingulacea derived through Lingulidae. Ordovician and 

 Silurian. 



Lingtilops Hall. Small Lingulids with narrow, depressed, not excavated 

 platforms. Ordovician and Silurian ; North and South America. 



Lingulasma Ulrich (Lingidelasma Miller). Large thick-shelled Lingulids 

 with very prominent, slightly excavated platforms. Ordovician ; North 

 America ; (1) England. 



Order 2. NEOTREMATA Beecher. 



Derived and specialised inarticulate Brachiopoda, probably developed 

 through Biciinae of the Atremata. Shells as a rule more corneous than 

 calcareous, more or less cone-shaped, with the pedicle emerging through a 

 perforation or sheath in the ventral valve, or through a triangular more or 



