TRENTON LIMESTONE. 71 



108. 6. STREPTOPLASMA PARVULA (n. .?p.). 



I'L. XXV. Figs, 4 a, b, c. 



Turbinate, curved, somewhat gradually expanding above ; cup deep, occupying about 

 one half the length of the specimen ; lamella; few ( about 30 ) , strong ; surface smooth ; 

 edge of tlie cup not recurved. 



This species is nmch smaller than either of the preceding, and, presenting a nearly 

 smooth surface, differs externally from the young specimens of S. corniculum. The lamellae 

 are also fewer than in that species, and are comparatively thinner and weaker than in S. 

 crassa. In many instances the margin is broken oil' to the depth of the cup, showing the 

 lamella; in the centre as high as on the outer margin, but this is always due to accident. 



It is much more numerous than either of the i^receding species, and is rarely associated 

 with them in the rock. 



Fig. 4 a. The lower part of a specimen of ordinary size, with the margin of the cup broken off, showing 



the lamellce within. 

 Fig. 4 b. Transverse section of the same, showing the simple radiating lamells. 

 Fig. 4 c. A group of the same. Three of the specimens lie upon the surface of the stone, with their 



bases nearly in contact. 



Position and locality. In the thin shaly layers just above the Birdseye limestone, at 

 Middleville, Herkimer county. - ^ (State Collection.) 



109. 1. PORITES"? VETUSTA (n. syj.). 



Pi,. XXV. Figs. 5 a, 6. 



A sub-hemispheric coral, composed of irregular concentric laminae ; cells vertical to the 

 laminae ; openings upon the surface, nearly circular, \vith internal vertical lamella which 

 reach half way to the centre. 



To some extent, this specimen presents the character of Porites, in a great degree of 

 perfection. The surface of the specimen being weathered, the radiating lainelhe are often 

 obliterated. The centre of the cells are also destitute ( perhaps from weathering) of the 

 fine elevated points characteristic of some recent species of the Porites. 



This is the only species known to me in the lower term of our system, which presents, 

 in any degree of perfection, the characters of the recent Porites. 



Fig. 5 a. Surface of the specimen, a part only showing the cells. 



Fig. 5 i. A portion magnified. The figure on the right hand is one of the cells more distinctly enlarged. 



Position and locality. In the lower part of the Trenton limestone, near its junction with 

 the Black-river limestone. Watcrtown, Jefferson county. 



