The !^^EW Species of Bkachiopoda. 351 



Triplecia Niagarensis. 



Plate 7, figs. 1-d. 



Triplecia Niagarensis. Hall. Palaeontology of N. Y., vol. VIII, pt. 2, expl. 

 pi. Ixxxiii, figs. 16-20. 1894. 



Shell of medium size with biconvex valves, the pedicle-valve 

 having a deep median sinus, and the brachial an elevated fold. 

 The brachial valve is much the more convex. Both lateral 

 slopes and median fold and sinus are plicated by well-defined 

 rounded ribs. 



Niagara dolomites. ]!^ear Milwaukee, Wisconsin. 



Christiania subquadrata. 

 Plate 6, figs. 13-18. 



Leptcena subquadrata, Hall. Rept. State Geologist N. Y. for 1882, pi. (xv) 



46, figs. 32, 33. 1883. 

 Christiania subquadrata, Hall. Palaeontology of N. Y., vol. VIII, pt. 1, p. 



351, pi. XV, figs. 32, 33; pi. xv a, fig. 36, and pi. xx, figs. 18-20. 1892. 



Shell small, elongate, semielliptical in outline, strongly con- 

 vexo-concave. Hinge-line short, straight, not equaling the greatest 

 diameter of the valves anteriorl}^. In the pedicle-valve the 

 umbo is full, rounded and incurved, with the apex obscure ; the 

 cardinal area is moderately broad and bears an open delthyrium 

 which terminates above in a circular foramen. The teeth are 

 short, divergent and continued into ridges which form the lateral 

 margins of two linguiform, muscular scars, traversing the shell 

 for almost its entire length. These scars inclose two much shorter 

 impressions. In the brachial valve the area is narrow, the cardi- 

 nal process bipartite on its anterior face, each of the lobes being 

 grooved behind. The crural plates are very long and divergent, 

 the upper portion of each terminating in an elevated extremity; 

 the lower portion produced on each side as a strongly elevated 

 ridge, curving slightly inward on the sides, then outward on 

 approaching the anterior margin of the valve ; each branch 

 recurving and passing backward, parallel to the median axis, as 

 far as the base of the cardinal process. The symmetrical spaces 

 thus formed are each divided transversely by a somewhat lower 

 vertical ridge. Between the inner muscular walls in the median 

 line is a low, rounded, longitudinal ridge. 



