CORALS AND BRYOZOA 



LOWER HELDERBHRG GROUP. 



DESCRIPTIONS OF SPECIES. 



STREPTELASMA, Hall. 1847. 

 Streptelasma stkictum. 



PLATE I, FIGS. 1-10. 



iStreptela*ma {Petraia) Hricta, Hall. Twenty-sixth Rept. N. Y. State Miis. Nat. Hist., j). 114. 1874. 

 stricta. Hall. ThiHy-se(-(Hi.l Rejif. N. Y. State Mus. Nat Hist., p. 142. 1879. 

 " strictuin, H \Lh. Report of State Keolog'ist for 1882. Kxpl. pi. 1, tig-s. 1-10. 1888. 



CoRALLU.M .simple, conical, very gradually and regularly enlarging; straight or 

 very slightly curved, except at the apex, which i.s sometimes more a?jruptly 

 bent. Exterior marked with strong undulations of growth and numerous 

 fine concentric striae ; external rays very prominent, from forty-five to fifty 

 at a point where the diameter of the corallum is 15 mm.; the increase 

 in number taking place usually at three distinct points, but sometimes at 

 only two. 



Calix deep, sides thin and nearly erect; a flat space at the bottom. 

 In one calix, having a diameter of 20 mm., there are fifty-four lamellae ; 

 alternate lamella) extending only a short distance from the walls at the 

 base of the calix and frequently coalescing with the primary lamellae. 



