58 
ANNALS NEW YORK ACADEMY OF SCIENCES 
From this study of the species it is seen that Streptelasma corniculum can 
easily be derived from the S. profundum type. The principal differences lie 
in its larger size, more robust growth, larger number of septa corresponding 
with the increase in size and more nearly radial arrangement of the septa. 
Another fact to be noted is that the counter quadrants are accelerated in 
development over the cardinal quadrants, there being at least three more 
pairs of septa in the counter quadrants than in the cardinal. 
Streptelasma rusticum Billings. 
1851 Streptelasma corniculum Edwards & Haime, Mon. Poly. Foss, des Terr. 
Pal., pi. 7, fig. 4. 
1858 Petraia rustica Billings, Geol. Sur. Canada. Report of Progress, 1857, 
p. 168. 
1875 Streptelasma cornicula Nicholson, Pal. Ohio, vol. II, p. 218. 
1882 Streptelasma rusticum Hall, 11th. Rept. State Geol. Ind., p. 376, pi. 51, 
figs. 2-4. 
1891 Streptelasma rusticum Winchell and Schuchert, Geol. & Nat. Hist. Sur. 
Minn., vol. Ill, p. 93. 
This species, throughout the earlier stages of its development, is identical 
with S. corniculum. It, however, attains a much larger size, and in the 
later stages of development becomes almost cylindrical in manner of growth. 
Winchell and Schuchert were probably the first to point out that a line of 
development could clearly be traced in S. profundum, S. corniculum and S. 
rusticum} 
Enterolasma caliculum Hall. 
1852 Streptelasma calicula Hall, Palaeontology of New York, vol. II, pi. 32, 
fig. la-k. 
1900 Enterolasma caliculum Simpson, Bull. 39. New York State Museum, p. 
203-205. 
Throughout the Siluric, although individuals are very numerous, the 
number of species representing the Streptelasma line of development is 
very limited, Enterolasma caliculum being the only really important one in 
this whole period. 
Enterolasma is a genus proposed by Simpson in 1900 iloc. cit .) for certain 
species previously included in the genus Streptelasma. The feature on 
which the generic distinction was based was the presence of a peculiar 
pseudocolumella. The author’s generic description is as follows: 
1 Geol. & Nat. Hist., Sur. Minn., vol. Ill, pt. I, p. 87. 
