OF CONCHOLOGY. 83 



T. minor, n. s ? Plate 11, fig. 6. ifr 



Characterized by the narrow median groove of the false area, 

 and the striae stronger outside of this than inside ; the apparent 

 absence of any lateral ridges or gutters on the area ; the septum 

 rising above the anterior part of the lamina in the median line ; 

 the flat but proportionally more elevated neural lamina and the 

 straighter beak ; a slight but conspicuous median flexure occurs 

 in the anterior margin of one specimen, and is nearly wanting in 

 the other. 



Locality. Guelph limestone, Gait, Canada, E. Billings, 1857. 



One certainly (and one probably) neural valve were received 

 from Mr. Billings. There is a possibility that this may prove to 

 be a form of the last species, but the character of the area ap- 

 pears very different. A much larger and more perfect series is 

 needed to determine the specific range of these protean shells. 

 It is certainly a Trimerella. 



Trimerella conradi, Hall. 



Obolus conradi, Hall, 20th Regents Rep. on the State Cabinet, ' 

 p. 368, PI. 13 (4), f. 1, 2, 1867. 



This species is probably a Trimerella, as Pr of '. Hall inferred in 

 his description, though at that time, in deference to the opinions 

 of Messrs. Davidson ;md Woodward, he placed it in* the genus 

 Obolus. It appears to differ from any of the other species here 

 mentioned, in its broadly transverse shell, very short beak, and 

 the form of the internal plates. 



Locality. Leclaire limestone, upper Niagara group, at Leclaire, 

 Iowa ; and in a similar deposit at Racine, Wisconsin. Hall, loc. 

 cit. 



T. ohioensis, Meek. 



T. ohioensis, Meek, Sill., Am.'Journ. Sci. and Art. p. 305, 

 April, 1871. 



Characterized by the strongly flexed posterior margin and 

 deeply incurved haemal beak ; large and very prominent tubular 

 processes, almost equally so in both valves ; the anterior end of 

 the septum raised and rounded, very prominent, the anterior 

 ends of the cylindrical processes flaring and oblique, the upper 

 edges overhanging and effuse. 



Locality. Niagara limestone, Genoa, Ottawa Co., Ohio. Sink- 

 ing Springs, Ohio, I. S. Newberry. Guelph limestone, Canada ? 

 one valve, E. Billings. 



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