122 
PROCEEDINGS OF THE ACADEMY OF 
This shell suggests Terebratula pleurodon, variety polyodonta, Phillips, 
(Greol. Yorks, pi. ii. p. 222, pi. xii. fig. 27.) It is a smaller species than that, 
with a shallower sinus and an abruptly deflected margin. 
Rhynchonella unica, n. sp. Sli&ll minute, longitudinally ovate in outline, 
the sides and front equally rounded, the cardinal slopes somewhat straight 
and the beak acute. The peculiarity consists in the arrangement of the me¬ 
dian plications of the two valves. In the middle of the ventral valve are five 
sharp plications which extend to the beak ; the two outer of these are very 
prominent, projecting above the general surface like vertical laminae; the 
middle three are anteriorly depressed considerably below the general surface, 
and constitute the mesial sinus, which extends to the middle of the valve, 
and thence rises above the general surface to the level of the two outer plica¬ 
tions. On each side of the median plications are four others, which, instead 
of converging toward the beak in conformity with the median ones, converge 
toward an imaginary point some distance in front of the beak, in consequence 
of which the posterior extremities of two or three are overlapped by the median 
set. In the dorsal valve four median plications rise in an elevated band and 
attain an equal elevation near the front of the valve, but posteriorly, the two 
middle ones of the four sink below the level of the others, and are lost from 
sight before reaching the beak. In consequence of these arrangements, the 
ventral valve presents a sinus anteriorly and an elevation posteriorly ; while 
the dorsal valve presents an elevation anteriorly and a sinus posteriorly. 
The two valves are about equally convex. The beak of the ventral valve 
projects in a tabular form slightly beyond that of the dorsal, and exhibits a 
circular perforation of the extremity. 
Length, *24 (100) ; breadth, *19 (79) ; thickness of both valves, -15 (62). 
From Bed “ No. 4,” Burlington, Iowa. “ White Collection ” of the Univer¬ 
sity of Michigan. 
Rhynchonella (Retzia ?) micropleura, n. sp. Shell of medium size, Retzia- 
like externally. Ventral valve ovate, somewhat produced rostrally, with 
rather straight lateral margins, and a semi-circular anterior margin; most 
tumid near the beak, slightly flattened anteriorly ; beak somewhat incurved ; 
mesial sinus wanting or represented only by a slight flattening of the anterior 
portion ; surface with two or three varices of growth, and about 50 rigid, con¬ 
tinuous, rounded, radiating ribs, which are separated by narrower spaces. 
! ' ?i 7 Length of ventral valve, *59 (100) ; width, *48 (81) ; convexity, -15 (25). 
Collected by A. Winchell, at Battle Creek, Michigan. 
It much resembles Retzia polypleura , Win., of the Huron group, but the 
beak is less prolonged and less straight, and the width of the shell is greater. 
1 know of no Rhynchonella which like this is without a sinus, and so finely 
ribbed at the same time. In the first of these characters it is approached by 
R. Hubbardi and R. Sageriana, from the same rocks. 
Rhynchonella Hubbardi, Win. This species originally described from Mar¬ 
shall and Pt. aux Barques, Michigan, has since been found by the writer at 
Napoleon Cut in Jackson county ; and also rather plentifully in some of the 
thin layers of sandstone at Valley Forge, near Cuyahoga Falls, Ohio. It’ oc¬ 
curs also at Talmadge, Summit county, Ohio, in beds next below the conglo¬ 
merate. Whittlesey’s collection. 
Rhynchonella Sageriana, Win. Identified in Whittlesey’s collection from 
Weymouth, Medina county ; near Ashland, Ashland county ; Drew’s saw¬ 
mill, Big Brook, Orange, Cuyahoga county, and two miles southwest of North- 
field Centre, Summit county, Ohio. 
R. iSageriana has remote relations to some of the forms of R. pleurodon, 
Phillips. Compare var. L>ev r euxiana, De Kon. (Davidson’s Mono. Brit. Carb. 
