286 PALEOZOIC PALEONTOLOGY. 
: RHYNCHOTRETA TRANSVERSA MN. Sp. 
Plate XXIX., Figs. 32-39. 
Description.—Shell small, broadly subtriangular, valves subequally 
convex, greatest width anterior to the middle, the postero-lateral slopes 
flattened, meeting at the beak in an angle of less than 90°. Pedicle 
valve depressed-convex, the beak slightly attenuate, sharply pointed, 
erect, the delthyrium broadly triangular, the median portion of the 
valve depressed anteriorly in a shallow sinus. Brachial valve depressed- 
convex, the median portion shghtly elevated in front in an indefinite 
fold, the beak sharply incurved. The surface of each valve marked 
by from seven to nine simple, angular plications, which continue to 
the beak, one being included in the sinus of the pedicle valve and two 
elevated in the fold of the brachial valve. 
The dimensions of a very perfect individual are: length, 5.5 mm. ; 
width, 6.5 mm.; thickness, 2 mm. Those of another more mature 
specimen are: length, 6 mm.; width, 7.5 mm.: thickness, 3 mm. 
Remarks.—In its sharply-pointed, erect beak, in the form of the 
delthyrium and in the flattened postero-lateral slopes, this little shell 
resembles Rhynchotreta cuneata of the Niagaran faunas, and the two 
shells are believed to be cogeneric. It differs from the Niagaran shell, 
however, in its smaller size and its greater proportionate breadth. The 
species is not uncommon in the higher beds of the Coeymans limestone 
near Hainesville, but has not been observed elsewhere. 
ATRYPA RETICULARIS (Linn). 
Plate XXX., Wigs. 11-18. 
See, also, pp. 2386 and 3869. 
Description —Shell subelliptical in outline, longer than wide. 
Pedicle valve depressed-convex, with a shallow, rounded mesial sinus 
extending from near the middle to the front margin; beak small, 
pointed, closely incurved over that of the opposite valve. Brachial 
valve gibbous or ventricose, its greatest convexity a little back of the 
