154 Trans. Acad. Sci. of St. Louis. 
to comprehend the motives for this association. In Surcu- 
Joma the beak is rather slender and somewhat abruptly formed 
below the convexity of the body whorl, the ribs large and few 
in number, the spire whorls always more or less angulate in 
profile at the periphery and the sculpture invariably consists 
of minute and very close-set spiral lines. In Amblyacrum, 
however, the beak is thick and gradually formed, the ribs 
numerous and close-set, the spire whorls almost evenly arcuate 
in profile and the spiral sculpture coarse and not close-set. 
The general facies of the shell in the two genera is wholly differ- 
ent. There are four species of Surculoma known to me at pres- 
ent, described under the names tabulata Con. (—=coelata Lea) — 
assumed as the generic type — from the Upper Claiborne sand 
and penroset and dumblei, of Harris, and stantoni Vaughan, 
from the Lower Claiborne of Texas and Louisiana. Penrosei 
Harr., which was published by its author as a variety of 
huppertzi, is in no way closely related to that species, having 
a radically different embryo as well as a different position of 
the anal sinus. Dumblei is more slender and has a relatively 
higher spire and shorter aperture than the others, but does 
not differ otherwise. Subaequalis, of Conrad, may possibly 
be an aberrant species of this genus, although the periphery 
is decidedly more obtuse; it seems to have the same peculiar 
minute close-set spiral lines, which, inall the species, alternate 
with larger lines toward base; it is very stout in form, with 
short obtuse rounded ribs, the aperture and short slender 
canal together being fully as long as the remainder of the 
shell if not longer. The embryo is wanting in the type and 
apparently only known specimen, which is from the Upper 
Claiborne sand. A very large and conspicuous umbilicus 
occurs in fabulata as an abnormal character. 
Microsurcula n. gen. 
This genus is composed of aconsiderable number of species, 
all of which are very small, with the body whorls seldom ex- 
ceeding four in number at maturity. The embryo is relatively 
large and complex, conical, multispiral, closely coiled and 
with about five whorls, the lower one to three of which are 
