GASTROPODA. 959 
Synopsis of Pleurotomariida.] 
XV. Hormortoma, Salter, 1859.* Shell elongate, beaded, practically imperforate, 
composed of rather numerous (eight to fourteen) rounded or swbangular whorls; 
aperture acuminate subovate, narrow and more or less prolonged below; outer lip 
with a broad and deep >shaped notch and no slit; band median or submedian, 
generally obscure, of moderate width, flat or slightly concave, in the perfect condi- 
tion margined on each side by a delicate raised line; surface marked with lines of 
growth only; these are never very sharp and always sweep backward very strongly, 
from below especially, to the band. Type, H. salteri Ulrich [—M. (1) gracilis 
Salter, not Hall]. 
XVI. Cexocavius, @hlert, 1887. Similar to Hormotoma but the shells are 
longer, and composed of more numerous depressed whorls. Axis perforate, the 
umbilicus small but extending quite to the apex. Aperture rounded, not produced 
below; inner lip thin. Type, Murchisonia (Colocaulus) davidsoni Ehlert. 
XVII. TURRITOMA, n. gen. (Ulrich.) High shells, consisting of numerous 
whorls; whorls somewhat flattened, convex above, slightly concave in the middle, 
and most prominent in the lower part where the band is situated; other features 
apparently as in Hormotoma. Type, Murchisonia acrea Billings. Range, Lower and 
Upper Silurian. 
This is a well marked group of species and readily distinguished form Hormo- 
toma (to which the group is related) by the flattened instead of uniformly rounded 
volutions, and by the lower position of the band. For the present the new genus 
will include the following species: Murchisonia ada Billings, Calciferous; M. acrea 
Billings, Quebec; M. laphami Hall, Niagara; M. boylei Nicholson, M. constricta 
Whiteaves, Guelph; and M. cava Lindstrom, Upper Silurian of Gotland. 
XVIIL Sorenosprra, n. gen. (Ulrich.) Small shells usually, forming a high and 
very slowly enlarging spire, consisting of numerous, generally depressed volutions; 
near the middle of each whorl and occupying nearly a fourth of its hight, the spiral 
band forms a deep channel between two salient thin ridges; the flat or convex slopes 
above and beneath the band may be free of ridges, or there may be a third above 
and a fourth below, or there may be, including those bordering the band, as many 
as five or even six on each whorl. Outer lip with a broad >shaped sinus but no 
linear slit. Type, Hunema pagoda Salter. 
Doubtful and insufficiently known generic and minor groups of Paelozoic species usually 
referred to Pleurotomaria and Murchisonia. 
Murcuisonta, d’Archiac and Verneuil, 1841. (Bull. Soc. Géol. France, vol. 12, 
p- 154.) We prefer not to give a description of this genus at this time, because 
*Canadian Organic Remains, Decade I, p. 18. 
+ Extr, Bull. Soc. d’Etud. Scientif. d’Augers, p. 20. 
