Streptelasinu.l 



SPONGES, GEAPTOLITES, CORALS. 87 



Section MADREPORARIA RUGOSA. 



Family STREPTELASMID^E, Nicholson.* 



STREPTELASMA, Hall. 



1847. Streptopluama, HALL. Palaeontology 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. Palaeontology of Ohio, vol. ii, p. 21. 



1889. Streptelasma, NICHOLSON. Manual of Palaeontology, vol. i, pp.247, flg. 127B; 278, 279, fig. 



156 A, B ; 280, flg. 157 ; 297, flg. 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 fossulse and a more or less prominent counter septum, sometimes straight, 

 slightly bent or strongly twisted and obscuring the fossulse 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 fossulae ; counter septum sometimes very prominent. " The lower part 

 of the visceral chamber is more or less extensively filled up with stereoplasina, and 

 the upper part of the same is crossed by irregular tabulae, 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 fossulae and 

 there forms a small pseudocolumella. In S. rusticum 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 PlajontoloKy, vol. i, p. 297. 



