128 
IOWA ACADEMY OF SCIENCE Voi,. XXIX, 1922 
of a very interesting Eurypterid. The carapace is sub-semicircular 
in outline ; anterior margin well rounded ; posterior margin broad- 
ly concave ; sides diverging gently posteriorly and somewhat pro- 
duced at the postero-lateral angles. The compound eyes are promi- 
nent, bean-shaped, situated about in the middle, and as far apart 
as their distance from the outer edge. Length, 8 mm., width, 13 
mm. The species is named Eurypterus thomasi in honor of Prof. 
A. O. Thomas. 
Department oe Geology, 
State University oe Iowa. 
ORIGIN OF LIMESTONE CONGLOMERATES 
LOUISE FILLMAN 
A study of the literature reveals at least eight ways in which 
limestone conglomerates may be formed. The following ways 
are noted and described in the paper : ( 1 ) derivatives from some 
pre-existing rock; (2) by deformation of the laminse; (3) by 
pebbles derived from concretions; (4) by the secretions of lime- 
stone nodules by algae; (5) by the breaking of thin layers of 
limestone by storm waves; (6) by subaquatic gliding of limestone 
layers; (7) by lime-mud being cracked on a tidal beach; (8) by 
minor oscillations of the sea and the erosion of materials previously 
deposited. 
CLASSIFICATION OF LENSES 
LOUISE FILLMAN 
This paper is the result of a bibliographic study of lenses, on the 
part of Lloyd North and the writer. In the literature some thirty- 
two genetic types are described. In the present paper these types 
are classified and described. A bibliography is appended. 
Department oe Geology, 
State University oe Iowa. 
THE ROCKFORD GEODES 
S. L. GALPIN 
These geodes occur in Lime Creek shales. They are rather 
unusual in containing a number of roundish cavities rather than 
the customary rough opening. The cavities are lined with : 1, small 
