TRIGERIA 245 



Remarks. The brachidium has been observed in but a single example 

 of this shell, the interior of which specimen is filled with nearly trans- 

 parent calcite. In this specimen the brachidium is apparently complete 

 and seems to agree with that of the genus Selenella, with which genus 

 the external form of the shell also conforms. In some respects these 

 little shells have the appearance of young individuals; this is especially 

 true in the almost complete absence of concentric lines of growth and 

 in the immature condition of the pseudodeltidium, the small size is also 

 indicative of immaturity, but there is no larger species of loop-bearing 

 shells associated with this one in the Louisiana limestone fauna, of which 

 it might be the immature representative. The specimen whose dimen- 

 sions have been given above is the largest one observed by the writer, 

 the smaller ones are 1 mm. or less in length, with all gradations between, 

 the specimen in which the brachidium has been observed being one of 

 the larger ones. 



Horizon. Louisiana limestone. 



Genus TRIGERIA Bayle 



Description. Shell small, centronelliform, with subplano-convex valves, 

 marked with simple, radiating plications. Internally the brachial valve 

 has an undivided, tripartite hinge-plate, the median division being per- 

 forated near the apex. The brachidium as in Centronella but with a 

 smaller anterior plate. 



Remarks. The internal characters of the single member of this genus 

 here recognized, are not known, so that it is not possible to determine 

 whether or not it is truly congeneric with Trigeria guerangeri, the genotype. 

 It is, however, a plicated centronelliform shell and may be retained in 

 this genus where it was originally placed, uutil a knowledge of its in- 

 ternal characters shall prove that it belongs elsewhere. 



TRIGERIA (?) CURRIEI Rowley 

 Plate XXX, Figs. 30-33 



1901. Trigeria (?} curriei Rowley, Am. Geol., vol. 27, p. 350, pi. 28, figs. 



40-42. 

 1908. Trigeria (?} curriei Rowley, Mo. Bureau Geol. and Mines, vol. 8, 



2nd ser., p. 80, pi. 17, figs. 54-56. 



Description. Shell minute, plicated, subovate in outline, longer than 

 wide, the greatest width near or in front of the middle, the anterior and 

 antero-lateral margins subsemicircular, acutely pointed posteriorly. The 

 dimensions of a perfect specimen are : length of pedicle valve 2.7 mm., 

 length of brachial valve 2.5 mm., greatest width 2.2 mm., thickness 

 1 mm. 



