 Sand-Boulders in the Drift in Central Missouri. t9 
ypical implacentals, prepared by alinjection, may be carefully 
spared with each other and with those of representative 
Historical Note—It is proper to add that the idea of recog- 
two antithetical groups according to the presence or ab- 
tence of a neuroccele, was first formulated by the writer, under 
the names c@lianata’and acelianata, on a slip dated November 
add caloneura and stereoneura are dated April 3, 1885, 
passage on page 416 in Bell's “ Comparative Anatomy and 
iology” (Philadelphia, 1885), commenting on the presence 
a cavity in the nervous axis of chordata, was first seen March 
13, 1886; but in January of that year, in lectures to students, 
aed ina letter to Prof. J. H. Comstock, the general scheme of 
ous classification was presented in substantially the 
m here given. 
SAND-BOULDERS IN THE DRIFT, OR SUBAQUE- 
es OF THE: DRIFT, IN CENTRAL 
i URI.: 
BY J. W. SPENCER, M.A., Pu.D., F.G.S. 
OCATION.—During the winter of 1883-84 deep excavations 
_Were made in the Drift for foundations of additional build- 
at the University of Missouri (lat. 38° 57’ N.; long. 92° 20° 
: The altitude is seven hundred and thirty-six feet above 
anid Mexico. The University is near the southern margiń 
~ Polling Prairie, bounded by the large valley of the Hurkson 
4.” SXcavated out of Lower Carboniferous limestones to a 
A of one hundred and sixty feet. 
do iological Associations —The large valley dates back to the 
Of the Lower Carboniferous epoch. It was subsequently 
= or less occupied by deposits of the Coal-Measures, which 
nce been removed, except in some embayments and trib- 
favines. Whilst these deposits are not found capping the — 
* walls of the valley, yet remnants occur farther away, . 
the Drift-mantle, over the elevations of the rolling 
as shown in a well at the Gardens, just east of the 
'» where the Carboniferous shales have a thickness of : 
a 
