108 CONTRIBUTIONS TO CANADIAN PALAEONTOLOGY. 



their place taken by dissepiments of unequal size, curving convexly up- 

 ward and inward toward the centre where they form in combination with 

 the inner twisted ends of the primary septa an axial, more or less cellu- 

 lose columella that projects as a boss from the bottom of the cup. Septal 

 fossette usually present. The arrangement of the septa tetrameral. 



Type species. — S. expansa, Hall. 



Range. — Cambro-Silurian, Silurian, Devonian. 



Streptelasma corniculum, Hall. 

 Plate VI., figs. 7, 7a, lb. 



Streptelasma {Strepto}ylasma) corniculum, Hall. 1847. Palseon. New York, vol. I. p. 69, 



pi. 25, figs. la-d. 

 Petraia Ottawaensis, Billings. 1865. Canadian Naturalist, new series, vol. II, p. 429. 

 Streptelasma corniculum, Eominger. 1876. Geol. Sur. Mich., Foss. Corals, p. 141 (pars), 



pi. LI, upper row, specimens from the Trenton formation 



only. 



Corallum simple, elongato-conical, curved, gradually increasing in size 

 from a pointed base until a maximum breadth of about 3 cent, is reached 

 in a length of between 6 or 7 cent., average size somewhat smaller. 

 Outer surface marked transversely by accretion ridges of rather variable 

 size and disposition. Epitheca complete with distinct longitudinal septal 

 furrows. Calyx moderately deep, with steep sides and a convex floor ; 

 its depth measured from the centre of its floor is equal to rather less 

 than one-third of the height of the corallum. Septa well developed, of 

 two orders, primaries and secondaries, alternating, numbering in all in 

 mature individuals from about ninety to one hundred and twenty, the 

 primaries reaching the centre with their inner ends twisted, the secondar- 

 ies extending but a short distance inward from the wall. The free edges 

 of the septa in the calyx are denticulated. Dissepiments at times having 

 the appearance, in longitudinal sections of the corallum, of true tabulae, 

 irregular, subordinate to the septa between which they curve upward 

 convexly toward the centre of the visceral chamber, where they lose their 

 individuality and form with the twisted inner ends of the primary septa 

 an axial area of cellulose structure. 



Localities. — Collected by Sir William E. Logan, in 18^5, at Paquette's 

 Rapids, Ottawa River, by James Richardson at the same place, and by 

 R. D. Ells and L. M. Lambe, from the vicinity of Douglas, Eganville and 

 Cobden, in 1896 ; Birdseye and Black River formation. Collected by E. 

 Billings, also by H. M. Ami in 1883, from the Trenton formation at Ot- 

 tawa, Ont. This species is mentioned (Rep. Palasont. Prov. Ontario, 

 1875) by Nicholson, as occurring in the Trenton limestone at Peter- 



