578 
and postulating unlimited divisibility lay pri- 
marily in his rejection of actual infinity and 
acceptance only of potential infinity. 
If it is one of the aims of mathematical 
history to set forth the successes and failures 
of leaders of mathematical thought, then the 
Aristotelean tract, “De lineis insecabilibus,” 
is worthy of the attention of mathematicians. 
Fortran Cazori 
UNIVERSITY OF CALIFORNIA 
SPECIAL ARTICLES 
JURA-CRETACEOUS STONEWORT AND LIM- 
NEAS, SUPPOSEDLY FROM ARKANSAS 
PRESERVED in the paleontological collections 
at Stanford University is a large block of 
white chert containing spore-cases of stone- 
wort, a siliceous freshwater algz and moulds 
and casts of Lymnea ativuncula and DL. con- 
sortis White,! two pondsnails originally de- 
seribed from the Jura-Cretaceous red beds, va- 
riously called the Morrison formation or 
Atlantasaurus zone, at Garden Park, eight 
miles north of Cafion City Colorado. 
The matrix consists of white siliceous mate- 
rial made up of compacted spicules of stone- 
wort. The surface is rusty and roughened 
from exposure but shows no sign of stream 
attrition. The specimen is accompanied by a 
note by J. F. Newson, mining engineer and 
former Stanford professor, stating that it was 
one of two large blocks unlike any rock in 
place in the vicinity, picked up on the J. L. 
Van Winkle ranch, east 4 section 6, township 
5 north, range 16 west, near the Arkansas 
river opposite old Lewisburg, Arkansas. 
If Dr. Newson is correct in supposing that 
no beds of similar rock outcrop nearby it is 
thought that the material was carried there or 
perhaps lost by one of the early exploring ex- 
peditions returning down the Arkansas river 
from Colorado. I have hoped to obtain in- 
formation on the subject fromthe distribution 
of siliceous rocks derived from stonewort re- 
mains in this region but they appear to be of 
such rare occurrences as to have escaped notice. 
1 White, C. A., Bull. 29 U. S. Geol. Sur., 1886, 
p. 20, Pl. IV., Fig. 8-9, consortis, 10-11, atwun- 
cula. 
SCIENCE 
[N. 8. Vou. XLVIII. No. 1249 
With the exception of the nutlets the re- 
mains of the Estancia stonewort, Chara estan- 
ciana Hannibal, are desiccated beyond recog- 
nition. These resemble the nutlets of the 
Bear River stonewort, Chara stantoni Knowl- 
ton,? but are nearly round and marked by 
six encircling spirals. 
There are three groups of limneas found in 
North America, the Abysmal limneas includ- 
ing Lymnea (Acella) haldemani Binney, the 
Moss limneas including Lymnea (Galba) 
truncatula Miill., humilis Say (+ cubensis 
P fr.), humilis solida Lea, obrussa Say, and 
coopert Hannibal and the Marsh limneas in- 
eluding Lymnaa (Lymnea) stagnalis L., colu- 
mella Say, auricularia L., palustus Mill. and 
the European glaber Mill. The Garden Park 
limnea, Lymnea ativuncula White, and Cation 
City limnea, Lymiwa consortis White, belong 
to the third group. 
These species are the oldest true limneas 
known from North America. JL. accelerata 
White of the Morrison beds is perhaps a 
Inoplax or other operculate while L. nitidula 
Meek of the Bear River Cretaceous is a prob- 
lematie species that has been confused by 
White? with some other Limnea, possibly the 
Eocene L. vetusta Meek. 
Harotp HAnniBaL 
San JOSE, CA. 
2 Knowlton, F. H., Bot. Mag., XVIII., 1893, p. 
141, text fig. 1-3; White, C. A., Bull. 128, U. S. 
Geol. Sur., 1895, pp. 63, 104, Pl. X., Figs. 14-16. 
3 White, C. A., Bull. 128, U. S. Geol. Sur., 1895, 
Pl. VI., Figs. 1-2 doubtful, Fig. 3 nitidula. 
SCIENCE 
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