318 



MOLLUSCOIDEA BRACHIOPODA 



SUB-KINGDOM V 



present in the pallial region. Cardinal process strong, curved, or erect, extend- 

 ing far above the hinge-line. Brachial ridges well defined. Extraordinarily 

 abundant in Carboniferous and Permian. Distribution general. 



P. giganteus is the largest Brachiopod known, sometimes attaining a width of nearly 

 one foot. 



Proboscidella, Oehlert. Valves very unequal ; dorsal valve small, concave, 

 operculiform ; ventral valve larger, convex, furnished with two lateral expan- 

 sions which bend downward to meet the margins of the dorsal valve, and an 



FIG. 532. 



A, Productus semireticulatus, Martin. Carboniferous Limestone ; Vise, Belgium. 1/1- -B> P- giganteus. 

 Martin sp. Same horizon ; England. Interior of dorsal valve (after Woodward). C, D, P. horridus, Sow. 

 Permian ; Prussia and England. !/! C, Interior of dorsal valve. D, Cast of ventral valve (A, Adductors ; 

 R, Diductors ; pr, Cardinal process ; h, Hinge-line ; v, Brachial impressions). 



anterior expansion, which is produced forward into one, or occasionally two, 

 long, cylindrical tubes. Carboniferous ; Europe and North America. 



Stheridgina, Oehlert. Shell very small, nearly as broad as long, and 

 attached to foreign bodies, notably Crinoids, by the spines of the ventral 

 valve. Dorsal valve with a small beak ; surface ornamented by concentric 

 flexuous plications bearing a few scattered spines. Carboniferous ; Scotland. 



1 Daviesiella, Waagen. Shell Productoid, but without spines and well- 

 developed cardinal area and teeth. England. 



1 Aulacorhynchus, Dittmar (Isogramma, Meek and Worthen). Very large, 

 transverse, thin shells with a ventral platform. Exterior surface with numerous, 

 regular, continuous, concentric ridges. Upper Carboniferous ; Europe and 

 North America. 



Family 7. Bichthofenidae. Waagen. 



Strophomenacea, probably derived through the Productidae, and remarkably modified 

 by ventral cementation. The form is that of Cyathophylloid corals with an operculiform 

 dorsal valve. Shell structure cystose. 



