SPONGES, GRAPTOLITES, CORALS. 87 
Streptelasma.] 
Section MADREPORARIA RUGOSA. 
Family STREPTELASMIDA#, Nicholson.* 
STREPTELASMA, Hall. 
1847. Streptoplasma, HALL. Paleontology of New York, vol. i, p. 17. 
1847. Streptelasma, HALL. Ibidem, corrections, p. 339. 
1857. Streptelasma, BILLINGS. Canadian Naturalist and Geologist, vol. i, p. 122, 
1875. Streptelasma, NICHOLSON. Paleontology of Ohio, vol. ii, p. 21. 
1889. Streptelasma, NICHOLSON. Manual of Paleontology, vol. i, pp. 247, tig. 127B; 278, 279, fig. 
156 A, B; 280, fig. 157; 297, fig. 178 A, B. 
Corallum simple, turbinate or conical, probably always slightly attached. 
Outer wall more or less thick, produced by the lateral thickening and fusing of the 
outer ends of the septa one with another. Septa numerous, prominent, alternately 
large and small, sometimes dentated along their edges, divided into four groups 
by three fossulz and a more or less prominent counter septum, sometimes straight, 
slightly bent or strongly twisted and obscuring the fossulz in the center of the calyx. 
Cardinal septum short or long dividing the most prominent or dorsal fossula cen- 
trally, which is situated on the convex side of the corallum ; alar septa short, situated 
in the lateral fossule ; counter septum sometimes very prominent. “The lower part 
of the visceral chamber is more or less extensively filled up with stereoplasma, and 
the upper part of the same is crossed by irregular tabule, dissepiments being also 
developed in moderate numbers. The center of the visceral chamber is [sometimes] 
occupied by a large, irregularly reticulated or trabecular pseudocolumella, with 
which the inner ends of the long septa are directly connected, and which is highly 
characteristic of the genus.” (Nicholson, op. cit., p. 298, 1889.) 
Type, S. expansa Hall. Species usually adopted as the type, S. corniculum Hall. 
A line of development can be traced clearly in S. profundum, S. corniculum and 
S. rusticum. The first species makes its appearance in the Birdseye and Black River 
groups, is generally straight in its growth with a deep visceral cavity and has reg- 
ular septa. This form passes into a larger and more or less strongly curved coral- 
lum, S. corniculum of the Trenton and Galena groups, the visceral cavity is less deep, 
being more strongly filled up with stereoplasma, and has a greater number of septa 
which in approaching the center become twisted obscuring the lateral fossule and 
there forms a small pseudocolumella, In S. rusticwm of the Hudson River group, 
the corallum attains to two or three times the length of S. profundum, while the 
septa are as a rule even more numerous and more strongly twisted, with a larger 
pseudocolumella than in S. corniculum, the entire lower portion of the coral is filled 
up with stereoplasma, 
*Manual of Pleontology, vol. i, p. 297. 
