OASTBOPOI'A 1017 



HOKMOTOMA BBI.I.K-lNVTv //"//. 



PLATE i.x x. FIGS u-rr. 

 HALL. 1847, Pal. New York, rol. I, p. 178, pi. xxxix, fig*, la and 16, ?le and 



Id, tlot 



to 45 mm., apical angle 42 to 60, generally about 44; volution* neatly rounded, some- 

 times appearing a littli- flattened in the upper half, rather closely wound, depressed so that the highland 

 width i ri-|-.-t!\.-ly as one Is to two, about six or seven in number, casts, however, rarely preserving 

 in .n- than f.iur : band wide, flat, clearly defined on shells, just above or exactly In the middle of th>> 

 whorls of the spire ; lines of growth strongly recurved to the band, regular, comparatively strong and dis- 

 tant, rarely visible on casts of the Interior ; a small, sometimes sharply defined umbilicus; apertun- 

 runded, except at the lower angle, which Is somewhat extended. 



At least two speclOH were united under the name Murchuoniu brllicinctu by Hall and most subse- 

 ! fni authors who have had occasion to write about the specie*, while collectors have used the name In a 



os and shifty manner. That Hall's original figures (toe. tit.) embrace at least two species must be 



a tn all who will take the trouble to compare his la and if. How could the former, representing a 

 small testlferous specimen, possibly be the apical portion of an example of the same species as the original 

 <>f the latter, which Is said to be an Incomplete "cast of a large specimen " T In the first place, the apical 

 angle of la Is about 50, while that of l< Is only about 32. So great a difference, especially In a genus of 

 shells In which the apical angle is unusually constant, almost certainly Indicates specific variation. 

 \vi,.-n we add that in corresponding parts of the two figures the one has four whorls where the other has 



tree, we may well wonder how the fact has so long escaped observation. Both forms occur In Min- 

 nesota, and our only difficulty has been to decide as to which Is the better entitled to retain the name 

 MMMM*. 



So far as known, neither occurs In any dtsvlslon of the Cincinnati period, and both appear to be 

 confined strictly to the Trenton proper. The larger form, however, seems to be the more common of the 

 two and therefore probably the form that has been the more frequently referred to by authors. On the 

 other hand, the smaller specie* precedes the larger on the plate, and, as the specimens figured of It are In 

 a better state of preservation than the other, It Is reasonable to assume that they furnished the greater 

 r the i-haracters brought out In Hall's description. We have therefore concluded to restrict the 

 application of the name Mlidntia to forms of the type of Hall's figs, la and 16, and propose a new deslg- 



i for the species represented by his fig. le. 



formation and locality. Not uncommon In the Trenton limestone In New York and Canada. In 

 Minnesota we have collected a total of eleven specimens, all from the lower part of the Fuslsplra bed at 

 various points In Good hue county. 



CWbetfom.-E. O. Ulrlch; W. H. Scofleld. 



HORMOTOMA TRENTONKN8I8, n. ap. 

 I-I.ATK LXX. FIGS. U and 14. 



Mitrdtaonia M/ieCneta (part.) HALL, 1M7, Pal. N. Y., vol. I, pi. xxxix, fig. l(not lo-ld); OWKN, 1862, 



p. VMs., Iowa and Minn., pi. n. fig. 8. 

 JfercUwiMa major WIIITFIKLD. 188Z, Owl. WIs., vol. Iv, p. 244, pi. ix. flg. 4 (not M. major HALL). 



it 30 to 100 mm., apical angle 38 to 37, generally about .15 : v.,iutmns seven or eight, almost 

 uniformly convex from suture to sutur > closely wound, with the hlght and width respectively as 



2 Is to 3 or 3 to 5; band median, wide, flat, the lunula; very moderately curved ; lines of growth r**ular, 

 fine, somewhat thread-like, avenging ax>ut eight In 5 mm., with the usual backward rur. , deep 



and wide; mouth greatly produced and turnl backward below; Inner lip thin, reflected, above partly 

 covering a small umbilical perforation. 



This beautiful shell has been for many years confused with H. MUeinela Hall sp. On the preceding 

 page we give our reasons for restricting MurrHUonia osOMneta to the smaller of the two species figured by 



