278 NORTH AMERICAN INDEX FOSSILS. 



LXX. Gypidula Hall. 

 Pentameroid, ventricose. Pedicle valve much the larger, with 

 or without a mesial fold ; cardinal area generally well defined, cross 

 striated ; spondylium unsupported for most of its length. Brachial 

 valve with or without mesial sinus ; spondylium large, sessile, acute 

 anteriorly. Siluric-Devonic. 



233. G. (Sieberella) galeata (Dalman). (Fig. 338.) 



Siluric? and Devonic. 



Subglobose. Pedicle valve gibbous with a mesial fold toward 



the front and a strongly incurved beak. Brachial valve gibbous 



above, with or without a mesial sinus near the margin. Surface in 



youth smooth but developing longitudinal plications in older forms. 



Fig. 338. Gypidula galeata (Pal. N. Y.). 



Differs from G. comis in its greater gibbosity, in the absence of a 

 distinct cardinal area, in the greater prominence of the plications 

 and in the greater incurving of the beak of the brachial valve under 

 that of the pedicle valve, thus concealing the delthyrium. 



Helderbergian (Coeymans) of New York, Pennsylvania, Mary- 

 land, New Brunswick, Northwest Territory. ? Niagaran of Indiana. 

 Middle Devonic of Europe. 



234. G. (Sieberella) pseudogaleata (Hall). (Fig. 339.) 



Lower Devonic. 

 Like G. galeata but differs in the absence of radiating plications. 

 Becraft of New York, etc. 



235. G. comis (Owen). (Fig. 336, c.) Middle Devonic. 

 Pedicle valve arcuate, with extended and strongly incurved beak ; 



delthyrium large and bordered by a distinct area. Surface cle- 



