MARYLAND GEOLOGICAL SURVEY 691 



The species is confined to the Monmouth and possibly to the Monmouth 

 of Prince George's County, but within that restricted area it is, with the 

 exception of Exogyra, the most conspicuous element in the bivalve faunas. 



Occurrence. MONMOUTH FORMATION. ? Bohemia Mills, Cecil 

 County; Brightseat, Brooks estate near Seat Pleasant, railroad cut west 

 of Seat Pleasant, ? 2 miles southwest of Oxon Hill, Fort Washington, 

 Prince George's County. 



Collections. Maryland Geological Survey, U. S. National Museum. 



Superfamily TELL1NACEA 

 Family TELLIN1DAE 



Genus TELLINA (Linne) Lamarck 

 [Prodrome, 1799, p. 84] 



Type. Tellina virgata Linne. 



:i The hinge of Tellina in the broad sense, when developed to the fullest 

 extent, comprises on each valve an anterior and posterior lateral and two 

 cardinals of which one is grooved or bifid on its distal edge. When the 

 valves are closed the two bifid teeth are central and the simple teeth are 

 respectively anterior and posterior to them. Normally the teeth of the 

 right valve close in advance of the teeth of the left valve, and in the obso- 

 lescence of the laterals those of the left valve disappear first. The simple 

 cardinal of the left valve is often very close to and hardly distinguishable 

 from the anterior part of the nymphal callosity, and owing to its fragility 

 is often broken off at the base, leaving hardly a trace, from which circum- 

 stances proceed the erroneous diagnoses so common in the literature 

 which ascribe a single left cardinal to sundry species or groups of Tellina. 

 No Tellina is without two cardinal teeth in each valve, and at least one 

 (anterior) lateral tooth in the right valve, unless it has been deprived of 



these parts by erosion, fracture, senility, or abnormal growth The 



ligament varies from extremely long and narrow, as in Phylloda, to short 

 and high, as in some species of Angulus. The nymphs are usually larger 

 and more prominent in thin shells with short ligaments ; subcircular species 



Etymology: TeXXtV?/, a kind of shell-fish. 



