129 



the lower bounding keel forming the greatest periphery of the 

 shell. Sculpture of equal, equidistant, primary spiral ridges, with 

 intermediate finer secondary ones, and the valleys concave, the 

 whole crossed by slightly oblique lines, dividing the surface into 

 a decussation of unequal rhomboidal spaces. 



Obs. — Phanerotrema is a genus established by Dr. Paul Fischer 

 to receive Pleurotoiuaria labrosa, Hall,* and other Pleurotomaroid 

 shells resembling it, such as Pleurotomaria balteata, Phill.f It 

 would appear to be a very necessary and good subdivision of the 

 larger and more comprehensive genus Pleurotomaria, and will 

 include those species with a rhoniboidally ovate form, and more or 

 less carinate body whorl, arising from the prominence of the band. 



Like P. labrosa, Hall, sp., our species attained a considerable 

 size, as evinced by the well marked, but imperfectly preserved 

 shell represented in PI. xix., fig. 4. It appears to be a more 

 obliquely elongated shell than P. labrosa, with a narrower band, 

 although larger in size, and a finer ornament. The American 

 species is from the Upper Pentamerus Limestone of New York 

 State, an horizon equivalent to that of the British Ludlow rocks. 



As regards the British species, P. australis, is decidedly a more 

 depressed shell with smaller upper whorls. The former is from 

 the Wenlock Limestone. 



Genus Murchisonia, d^Archiac and De Verneuil, 1841. 



(Bull. Soc. Geol. France, XII., p. 151.) 



Murchisonia, sj). irid. 



Obs. — Ill-preserved examples, either too impei'fect, or too much 

 defaced with matrix, to be determinable, are in the Collection. 

 The species has some points of resemblance with Jlurchisouia 

 cingidata, Hisinger, t but the angularity of the whorls and position 

 of the band do not coincide with those features of that species. 

 The same may be said of another allied shell M. sinuosa, Sby., 

 sp.§ Our species appears to me, on the other hand, to be allied 

 to Jlhirchisonia attenuata, His.,|| in which the band is nearly 

 median in position ; the only point of difference I am able to 

 indicate being the somewhat more angular whorls on the Gotland 

 shell. Otherwise the latter and our Murchisonia appear to be 

 closely allied. 



* Pal. N. York, 1859, III., p. 339, Atlas t. 66, f . 1 - 5. 

 t Mem. Geol. Survey Gt. Brit., 1848, II., Pt. i., p. 358, t. 15, f. 1—2. 

 X See Murchison's Geol. Eussia, 1845, Pt. iii., t. 22, f . 7a and b ; Lind- 

 strom's Sil. Gastropoda and Pteropoda of Gotland, 1884, t. 12, f. 9. 

 § Salter, Mem. Geol. Survey Gt. Brit., 1848, II., Pt. i.,p.357,t. 14, f. 2. 

 II Liudstrom, loc, cit., t. 12, f. 20 and 21. 



