GASTROPODA. 1057 
Cyclonema.] 
the two groups must have different roots. The oldest known shells (Stones River 
group) that are strictly referable to Cyclonema have relatively coarse revolving 
ridges. In our Strophostylus textilis, on the other hand, the revolving lines are very 
delicate. The difference is so marked that we cannot believe that Strophostylus 
came from the same immediate root as Cyclonema. In our opinion they represent 
two independent lines. 
The composition of the shell of Cyclonema must be different from that of the 
majority of Lower Silurian Gastropoda. On the hills about Cincinnati, where 
thousands of specimens have been collected, the test is preserved when all the other 
shells occur as casts of the interior only. Indeed, we have never seen a natural cast 
of Cyclonema. Another point worthy of notice is the extreme rarity of specimens 
retaining the apical nucleus. Out of considerably over one thousand good shells 
before us only six retain the apex entirely. In nearly all of the other cases the 
evidence at hand seems to show that these minute whorls were lost during the life 
of the shell, or, at any rate, before fossilization, while in four of the six specimens 
preserving them they were covered and protected by an encrusting bryozoan. 
The nuclei seen belong to four species, C. biliw var. fluctuatum, C. gracile, C. 
mediale and C. inflatum, the last of which may be but a well-marked variety of the third. 
In all the nucleus has a glassy appearance, with the first two whorls perfectly smooth, 
the third with distinct transverse lines only, and all three round and coiled so as to 
form a blunt apex to the shell. The generic and specific characters begin with the 
fourth whorl. In C. biliz and C. gracile the whorls decrease very gradually to the 
first two, but in C. inflatum the third and fourth whorls, witha part of the fifth, are 
wound into a subcylindrical coil oa top of the rapidly expanding succeeding 
volutions. In C. mediale the conditions may be described as intermediate. Consid- 
ering the character of the nucleus in these four representative species, it appears 
that the original stock from which Cyclonema sprang was a low-spired Holopea-like 
shell. 
So far, but a single true Cyclonema is known to us from Minnesota. Other 
Minnesota shells have been placed in the genus, but in our opinion they do not 
belong here. In order that the reader may get an adequate and just idea of the 
genus, and also that the genus may be properly established, we have decided to 
include a number of species that have not yet been found in the upper Mississippi 
region. 
Many species have been placed in Cyclonema that do not belong there. Some 
belong to Gyronema, as for instance, C. percarinatum Hall sp., C. semicarinatum Salter, 
C. nodulosum Lindstrém and C. carinatum (Sowerby) Lindstrém; others, like C. 
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