MISSISSIPPIAN LOOP-BEARING BRACHIOPODA 447 



plates well developed, retreating from the lateral margins of the 

 valve anteriorly and becoming differentiated into two portions, 

 a basal portion which joins the inner surface of the valve and is 

 directed obliquely inward, and a distal portion which is abruptly 

 bent in a subgeniculate angle so as to be directed obliquely out- 

 ward; the portion included in the angular bend of the two plates 

 is produced anteriorly into the bases of the crura, and just before 

 the crura become free a narrow transverse band joins their bases. 

 The characters of the brachidium not completely determined, but 

 it is believed to bs of the short, Dielasma-like type. Shell 

 structure finely punctate. 



Remarks. — In the arrangement of the internal features of the 

 apical portion of the brachial valve this genus is perhaps more 

 closely allied to Cranaena than to any other of the generic types 

 here recognized. It differs from Cranaena chiefly in the reduction 



«■ e y 



Fig. 7. — A series of six cross-sections (X2I) of the rostral portion of the brachial 

 valve of D. compressa (Weller). 



of the hinge-plate to a narrow, transverse band joining the crural 

 bases, while in Cranaena it is elongate, with a comparatively small 

 apical perforation, and with the crura originating as a pair of ribs 

 diverging anteriorly from near the apex. The difference in shape, 

 viz., the compressed shell and the erect beak of the pedicle valve, 

 are other features which easily separate the members of this genus 

 from all species of Cranaena which have been recognized. 

 Genotype. — D. compressa (Weller). Glen Park limestone. 



Rowleyella n. gen. 



Description. — Shell terebratuliform, with the valves subequally 

 convex. The beak of the pedicle valve perforated by a subcir- 

 cular foramen which encroaches wholly upon the umbonal region, 

 the delthyrium broadly triangular and wholly closed. Internally 

 each valve is supplied with a strong median septum which, in the 

 pedicle valve, reaches nearly to the center of the valve, that of 

 the brachial valve being; somewhat shorter. 



