Niagara Group. 411 



what compressed vesiculose appearance ; corallum consisting of thin, 

 superimposed lamina ; height 35 mm., diameter of the calix 60 mm. 

 depth 12 mm.; for a distance of 20 mm. from the margin it is gently 

 sloping, then nearly vertical ; a convex space at the bottom 15 mm. in 

 diameter ; tabula thin ; fossette small, deep, not extending on the 

 side of the calix ; number of lamellse 160, alternating in size, the smaller 

 ones rudimentary, not more than one sixth the thickness of the others ; 

 near the margin the larger ones are broad, angular, having a width 

 of about 1.50 mm. becoming thinner as they approach the center where 

 they are twisted and elevated, forming a false columella. 



This species has nearly the same form as P. fulcraium; it has also 

 similar processes for attachment, and might, on a cursory examina- 

 tion, be mistaken for that species, but it is much more distinctly 

 composed of thin, invaginated lamina?; the lamella? are. decidedly al- 

 ternating in size and there are well developed tabula?. 



Formation and locality. Niagara limestone, Louisville, Kentucky. 



HALLIA, Edwards and Haime. 



I have adopted the Genus Hallia of Edwards and Haime after 

 much hesitation and misgiving. Among the large collection of corals 

 from the Falls of the Ohio, the locality of the typical form of the genus, 

 I have not found a single specimen possessing the characters given in the 

 figure 3, pi. VI, of Polypiers des Terrains Palasozoique, and have been in- 

 clined to regard it as a possible modification of Aulacophtllum, of 

 which there are several species from that locality. There are, how- 

 ever, among the collections of the Niagara Group several forms which 

 cannot, with propriety, be referred to the Aulacophyllum or Strep- 

 telasma, but which possess the characters attributed to Hallia. 

 These forms are therefore, for the present, placed under this generic 

 term. 



Hallia scitula, n. sp. 



Corallum simple, small, broadly turbinate or patellate, rapidly ex- 

 panding, length of posterior side 5 mm., of the anterior side 8 mm.; 

 calix shallow, campanulate, diameter 15 mm., a flat or slightly con- 

 vex space at the bottom 5 mm. in diameter, with a small oval depression 

 at the center; number of lamellae 60, of nearly uniform size at the 

 margin, alternating below; commencing at the center and continuing 

 to the anterior margin is a single lamella more prominent than the 

 others, and to which about one-half of them converge, the remainder 

 continuing to the central depression. 



Formation and locality. Niagara Group, Louisville, Kentucky. 



