940 THE PALEONTOLOGY OF MINNESOTA. 
[Raphistoma. 
RAPHISTOMA, Hall. 
Raphistoma, HALL, 1847, Pal. New York, vol. i, p. 28. 
Raphistoma (part.) and Pleurotomaria (part.), of many authors. 
For the generic characters and a full discussion of the relations of this genus 
the reader is referred to the preceding remarks on the family. (See pages 931, 934.) 
Of the nineteen species referred to this genus in the last edition of Miller's 
catalogue, perhaps only R. stamineum and Rk. planistria, with its variety parvum, 
really belong here. The majority of the remainder must be classed as doubtful, 
since we do not know whether they have a slit-band or not. Some may belong to 
Raphistomina, as does R. lapicida Salter, or to Liospira, as do f. americanam Billings sp. 
— lenticulare Emmons) and R. subtilistriatum Hall sp. fk. niagarense Whitfield 
certainly is not a Raphistoma. It seems to be congeneric with Meek and Worthen’s 
Platyostoma trigonostoma. Two good species of the genus were described by Billings 
as Pleurotomaria calyx and Pl. crevieri, both from the Canadian Chazy. To these we 
add the two following new species. 
RAPHISTOMA PERACUTUM, 2. Sp. 
PLATE LXVIII, FIGS. 1—6. 
Shell small, not known to exceed 12 mm. in diameter, consisting of three or 
three and one-half whorls, flat above, rounded below; periphery very sharp and thin; 
umbilicus equalling a little more than a fourth of the greatest diameter, its edge 
narrowly rounded; hight of shell very slightly exceeding a fourth of the width. 
Surface marked on the flat upper side with very fine subequal strize sweeping on 
the whole rather strongly backward from the suture. About a third of the width 
of a whorl from the suture the striz are interrupted by a delicate revolving line. 
Between the latter and the extreme edge of the peripheral carina the striz make a 
distinct sigmoid curve. Below the periphery the surface is marked with similar 
strie, which, in descending, curve first forward and then almost directly toward the 
center of the umbilicus. 
In this species the hight is relatively less, and the peripheral edge consequently 
thinner, than in any previously described species of this genus. It is the only 
gastropod known to us as occurring in the Lower Silurian rocks of Minnesota 
having a perfectly flat spire. 
Formation and locality.—Black River group, Ctenodonta bed, Goodhue county, Minnesota. Rather 
rare. 
Collections.—E. O. Ulrich; W. H. Scofield. 
