308 MOLLUSCOIDEA—BRACHIOPODA SUB-KINGDOM V 
Thomasina, Hall and Clarke. Lingulae with the posterior margin of the 
ventral valve notched, and with two conspicuous articulating processes. 
Silurian ; France. 
Family 3. Lingulasmatidae. Winchell and Schuchert. 
Platform-bearing Lingulacea derived through Lingulidae. Ordovician and 
Silurian. 
Lingulops, Hall. Small Lingulae with narrow, depressed, not excavated, 
platforms. Ordovician and Silurian ; North and South America. 
Lingulasma, Ulrich. Large thick-shelled Lingulae with very prominent, 
slightly excavated platforms. Ordovician ; North America; (?) England. 
Order 2. NHOTREMATA. Beecher. 
Circular or oval, more or less cone-shaped, inarticulate Brachiopoda, with the 
pedicle opening restricted throughout life to the ventral valve. Pedicle aperture 
modified by a deltidium or listrium.  Prodeltidiwm attached to the ventral valve. 
Superfamily 1. ACROTRETACEA. Schuchert. 
Neotremata with phosphatic shells and a more or less well-developed deltidium. 
Dorsal protegulum marginal. Cambrian to Silurian. 
Family 1. Acrotretidae. Schuchert. 
Acrotretacea with the pedicle opening posterior to the protegulum. Cambrian to 
Silurian. 
Acrotreta, Kutorga. Ventral valve sub-conical; the posterior margin 
flattened, triangular in form, and resembling a true cardinal area. This 
slope is divided medially by a shallow groove, widening downward. Circular 
pedicle opening at the apex of the valve. Dorsal valve flat or depressed, 
convex ; interior flanked by a large anterior and a smaller posterior pair of 
muscular impressions ; exterior concentrically striated. Cambrian and Ordo- 
vician ; North America and Europe. 
Conotreta, Walcott. Small, highly conical shells, with the interior of the 
ventral valve marked by a number of radiating ridges. Ordovician and 
Silurian ; North America. 
Acrothele, Linnarsson. Rounded, or broadly oval, depressed shells with 
the cardinal area obsolete. Cambrian; North America and Europe. 
Linnarssonia, Walcott. Smaller and more conical shells than Acrothele. 
Cambrian ; North America and Europe. 
Discinopsis, Matthew ; New Brunswick. Jphidea, Billings ; North America 
and Sweden. Volborthia, von Moller; Russia. (?) Mesotreta, Kutorga ; Russia. 
(2) Orbicella, VOrbigny (Keyserlingia, Pander). (?) Helmersenia, Pander ; Russia. 
All Cambrian. 
Family 2. Siphonotretidae. Kutorga. 
Acrotretacea with the pedicle opening passing by resorption anteriorly through the 
protegulum and the wmbo of the shell. Cambrian to Silurian. 
