Upper Helderberg Group. 423 



mm., sides abruptly descending, at the bottom a conical elevation, 

 at the side of which is a fossette, which is a deep depression not defined 

 on the side of the calix ; number of lamellae 20, alternating in size, 

 thickened at the margin^ sharp below, the principal ones extending 

 to the center, twisted and coalescing, forming a false columella. 

 Formation and locality* Corniferous limestone, Canada West. 



Streptelasma ampliatum, n. sp. rL**h P/fA*"^ 



Corallum simple, turbinate, slightly curved ; walls thin ; acute at 

 the base, regularly and rapidly expanding to the margin ; length of 

 posterior side 32 mm., of anterior side 55 mm., diametor of the calix 

 50 mm., depth 40 mm., sides regularly sloping toward the center 

 where there is a prominent rounded elevation 10 mm. in diameter ; 

 fossette situated at the sinistral margin of the elevation, consisting of 

 a deep depression not extending on the side of the calix ; number of 

 lamellae 90, very slightly alternating in size, at the margin, thick, flat- 

 tened, becoming thin, sharp and more decidedly alternating in size as 

 they approach the center. The principal lamellae continue to the 

 center and are twisted and elevated, forming a false columella. This 

 species may be distinguished from Zaphrentis prolifica by the more 

 nearly uniform size of the lamellae, its more rapidly expanding form 

 and the different character of the bottom of the calix: from Z. fre- 

 quentata by the different form of the calix, and from both forms 

 by the absence of tabulae. 



Formation and locality. Corniferous limestone, Canada West. 



Streptelasma cokspicuum, n. sp. + l- 7 ^'' ^'ft- 

 Corallum simple, turbinate, base acute, regularly expanding to the 

 calix ; exterior with rounded annulations and undulations of growth ; 

 height 45 mm., diameter of the calix 30 mm., depth 20 mm., sides 

 sloping abruptly ; fossette dextral, conspicuous ; number of lamellae 

 from 80 to 90, alternating in size, 'the larger ones fasciculating, 

 coalescing and continuing to the center, very much thickened and 

 widened, often turned laterally ; sometimes coalescing at the center and 

 having the appearance of tabulae. This species may be easily recog- 

 nized by the great prominence of the lamellae at the center. 



Formation and locality. Corniferous limestone, Falls of the Ohio. 



Streptelasma fossula, n. sp. J*/,*-*/-. Fii f. 



Corallum simple, turbinate, curved ; exterior with prominent 

 rounded ridges of growth ; calix oblique, length of posterior side of 

 corallum 20 mm., of the anterior side 40 mm.; diameter of calix 25 

 mm., depth of anterior side 40 mm.; fossette consisting of a deep de- 

 pression just anterior to the center ; number of lamellae 72, alter nat- 



