EUMETRIA 439 



The shell structure is probably punctate, although this cannot be de- 

 termined from any of the specimens examined. 



Remarks. The minute surface markings and the shell structure of this 

 species cannot be determined from any of the specimens which have been 

 examined, because of their condition of preservation as more or less 

 modified casts in a fine-grained sandstone. In a few cases some more or 

 less indefinite, concentric lines of growth are retained, but for the most 

 part the specimens are essentially smooth, aside from the plications. 

 Neither the characters of the brachidium nor the peculiar characters of 

 the hinge of Eumetria have been observed in this species, and unless 

 individuals in a different condition of preservation than those at hand 

 are secured at some future time, there can be no hope of certainly deter- 

 mining the generic relations of the species. So far as external form, the 

 characters of the beak, and the characters of the cardinal area go, there 

 is no fundamental difference between this shell and the true species of 

 Eumetria from a higher horizon. The characteristic features of this species 

 are found in the broad plications, which are less in number than in any 

 other species except E. acuticosta, but which differ from that species in 

 being flat and rounded instead of acutely angular; the shell also has a 

 greater tendency to develop an undefined mesial sinus in the pedicle valve 

 than any of the other species, and the shell is usually somewhat more 

 pointed posteriorly. The small, intercalated, median plication which is 

 sometimes present in specimens of this species is also a character differ- 

 ent from that in any of the other species. 



The relationship of this species to the genus Acambona, and indeed the 

 relationship of the genus Eumetria to Acambona, is quite uncertain. Ex- 

 ternally the two genera are essentially alike, and although some of the in- 

 ternal characters of Acambona have been described as being entirely differ- 

 ent from similar parts of Eumetria, yet authentic specimens of Acambona 

 are so rare that it is most difficult to secure material from which to really 

 determine its essential characters, and it is not yet entirely certain that 

 the structures in Acambona have been correctly interpreted, or that there 

 is really an essential generic difference between it and Eumetria. If these 

 two genera should at some future time be proven to be synonymous, the 

 name Eumetria would have to give place to Acambona which has several 

 years priority. 



Horizon. Chonopectus sandstone of the Kinderhook. 



EUMETRIA OSAGENSIS (Swallow) 



Plate LXXVI, Fig. 12 



1860. Ketzia osagensis Swallow, Trans. St. Louis Acad. Sci., vol. 1, p. 653. 

 1894. Eumetria? osagensis Hall and Clarke, Int. to Study of Brach., pt. 

 2, pi. 37, figs. 7-9. 



