NO. 2297. BRACEIOFOD GENUS PLATYSTROPHIA—mcEWAN. 405 



DESCRIPTION OF SPECIES. 



1. UNIPLICATE GROUP. 

 PLATYSTROPHIA UNIPLICATA, new species. 



Plate 42, figs. 1, 2. 



Two specimens of a uniplicate PlatystropTiia were found in the 

 Trenton of Lake Champlain. They are small and have low rounded 

 folds on which are two plications which appear to originate in a point 

 at the heak and extend to the frontal margin with a deep widening 

 furrow between them. The shallow sinus is occupied by one median 

 plication which originates at the beak and extends to the frontal 

 margin. The lateral slopes are occupied by nine plications. 



Measurements. — 8.2 mm. along the hinge line, 12 mm. wide across 

 the middle, 9 mm, high, 7 mm. thick, 5.5 mm. sinal width, 3 mm. 

 sinal depth, 1 mm. fold depth. 



Occurrence. — Trenton limestone near Lake Champlain, New York. 



Holotype.—C&t. No. 66109, U.S.N.M. 



2. BIPLICATE GROUP. 



a. SITBGROUP A. 



PLATYSTROPHU PRECEDENS, new species. 



Plate 42, figs. 7. 8. 



A form occurring in relatively small numbers seems to represent 

 an intermediate development between the uniplicate group and sub- 

 group B of the biplicate group. 



It has three plications on the fold, two of which are primary and 

 appear to originate in a point at the beak, and one of which is a 

 secondary plication intercalated in a median position; while in the 

 sinus there are two secondary plications which have originated by 

 the bifurcation of the primary plication at the beak. 



It differs from PlatystropMa trentonensis , new species, in that the 

 median plication on the fold has not bifurcated, and in the absence 

 of the median intercalated plication in the sinus. 



Occurrence. — Trenton limestone, Lake Champlain, New York. 

 Curdsville limestone of tlie Trenton group, Mercer County, Ky. 



Cotypes. —Cut. Nos. 66111, 66112, U.S.N.M. 



PLATYSTROPHIA REG CLARIS Shaler. 



Plate 42, figs. 21. 22. 



Platystrophia regularis Shaler, Bull. Mus. Comp. Zool.. vol. 4, 1865, p. 67. 



Shaler's original description is as follows: 



Outline much the same as that of other members of the group. Socket valve one- 

 fourth more projecting than toothed valve ; hinge line a little less than diameter of shell, 

 three-fifths greater than distance from beak to border. That portion of the margin 



