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Genus SPIEIFER. Sowerby. 



[Etv. : Spira, spire; fero, to bear.] 



(1815: Mineral Conchology, Vol. II., p. 42. 1893: Pal. N. Y., Vol. VIII., 



Pt. II., p. 1.) 



Shell variously shaped, commonly very much wider than 

 long, radially plicated or striated, crossed by concentric 

 growth lines, which in some forms are lamellose or even 

 marked by spines. Hinge line generally long and straight. 

 Pedicle valve usually with moderately high area, with an 

 open delthyrium, the margins of which are prolonged into 

 stout simple teeth, supported by dental lamellae. Area of 

 the brachial valve lower. A calcareous brachidium in the 

 form of a double spire, whose apices are directed towards 

 the cardinal angles, nearly fills the cavity of the shell. 



Spirifer mucronatus. (Conrad.) (Fig. 114.) (Pal. 

 N. Y., Vol. IV., p. 216, PI. XXXIV.) 



Distinguishing Characters. — Medium size; low cardinal 

 areas; much extended, often mucronate, hinge line, giving a 



Fig. 114. Spirifer mucronatus. Dorsal (brachial) and ventral (pedicle) views of a 

 medium-sized specimen : dorsal and lateral views of different individuals (from Hall). 



width of from two to four times the height of the shell; 

 well-marked sinus in the pedicle valve, and fold in the bra- 

 chial valve, which is often flattened or grooved; radiating pli- 

 cations, the outer ones of which do not reach the beak, and 

 lamellose lines of growth, often thickly crowded near the 

 front ; short dental plates, and striated muscular areas. 



