'IRE FAUNA OF THE ST. JOHN GEOUP. 65 



part of the valve by a uarrow depressed flattened furrow, the rim of the right valve fits 

 within that of the left. 



The surface of the valves appears smooth to the naked eye, but is finely granulated 

 when viewed with a lens. 



This species is remarkable for its high relief and regularly elliptical contour, at first 

 glance it would be taken for the head-shield of a Microdiscus, from which the glabella had 

 been removed by abrasion. 



Length, 5i mm. Widlh, 4|- mm. 



Horizon and Locality. In the dark sandstones of Div. 1.6\ at Hanford Brook, St. Mar- 

 tin's. Not rare. 



BEYRICHONA, n. gen. 



Valves nearly or qiiite as wide as they are long, and wider in front than behind ; they 

 have a rudely semi-circiilar fhittened area, extending not more than half-way from the hinge 

 line ; the rest of the valve < ouA-ex, and most elevated near the middle of the valve, the 

 flattened area has several depressions which are not very prominent. 



There is no central ridge (properly so called) on the valve of this genus, but there are 

 two very small oblique ridges close to the hinge line, of which the anterior may be taken 

 to represent the median ridge; the posterior ridgelet becomes confluent with the inner 

 termination of the posterior ridge. 



The protuberances of the surface are not so strongly marked in this genus as in that 

 above described, or as in the true Beyrichiîe. 



Beyrichona papilio, u. sp. (Plate VI. Figs. 20, 20a. and b.) 



Subtria ngular, acutely triangular toward the base, rounded in toward the hinge line at 

 each end. Depressed area faintly marked, except toward the hinge-line, where it is made 

 more prominent by the elevation of the anterior and posterior ridges ; the rest of the valve 

 is tumid, especially in the middle and toward the lower triangular extension of the 

 valve. 



The anterior furrow is triangular, narrow and deep in front, expanded and shallow 

 behind ; it is directed toward the middle of the posterior side of the valve and extends 

 nearly half way across the valve. The posteror furrow is subtriangular, and is parallel in 

 direction to the anterior furrow ; it is narrow and distinct in front near the hinge line, 

 and fades out toward the posterior slope of the valve. 



The median ridge is low, short, narrow, very oblique, and fades out behind the tumid 

 central part of the valve. The anterior ridge is narrowly triangular, and vanishes on the 

 elevated centre of the A^alve, about two fifths of the length of the valve from its lower 

 pointed extremity. The posterior ridge is rounded, and extends scarcely one third along 

 the posterior side of the valve ; it has a tuberculous elevation at the posterior angle of the 

 valve, around which it turns and, as a depressed and narrow ridge, runs forward along the 

 hinge line nearly half-way to the front of the valve. 



The margin of the valve in this species does not show a distinct fold. 



The surface appears smooth to the naked eye, but finely granulated under the lens. 



Sec. IV., 18S5. II. 



