374 



MOLLUSCOIDEA 



PHYLUM V 



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

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



Pseudolingula Mickwitz. Has a ventral pedicle groove and a pair of 

 umbonal muscles. Ordovician and Silurian ; Europe and America. 



Lingula Bruguiere (PAare^ra Bolton ; Lingularius Dumeril); (subgen. (r/ossma 



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 Dali. 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 



septal 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. 



Barroisella Hall andClarke. 



Silurian and Devonian ; North 



Lingula anatina Brug. Recent. A, Shell 

 with pedicle. B, Interior of ventral valve. 



551. 



Lingula lewisii Sow. 

 Sihman ; Gotland. 



Lingulids with rudimentary articulation. 

 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. Lingulids with a punctate shell. Devonian and 

 Lower Carboniferous ; North America. 



Family 2. Lingulasmatidae Winchell and Schuchert. 



Platform-hearing Lingulacea derived through Lingulidae. Ordovician and 

 Silurian. 



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

 platforms. Ordovician and Silurian ; North and South America. 



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

 with very prominent, slightly excavated platforms. Ordovician ; North 

 America ; (?) 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 triangulär more or 



