PART, ft CHAZYAN AND RELATED BRACHIOPODS—COOPER 645 
ROSTRICELLULA PLENA (Hall) 
Plate 120, I, figures 39-53; plate 132, D, figures 19, 20; plate 137, FE, figures 34-36 
Aitrypa plena Haut, Pal. New York, vol. 1, p. 21, pl. 4 bis, figs. 7a-c, 1847. 
Camarotoechia plena (Hall) Raymonp, Ann. Carnegie Mus., vol. 7, No. 2, p. 221, pl. 33, 
figs. 7-18, IQII. 
For full synonymy see Bassler, U. S. Nat. Mus. Bull. 92, p. 178, 1915. 
Attains a large size and is one of the biggest of the known species of this 
genus. Occurs in great abundance in the Valcour formation in the vicinity of 
Chazy and on Valcour Island. Raymond has discussed the variation of the 
species and concludes that Afrypa altilis and A. plicifera are variations of 
A. plena. 
The adult is generally subtriangular in outline, with the length and width about 
equal; maximum width at or a short distance anterior to the middle. Surface 
marked by 17 to 24 costae, 5 to 7 in the sulcus and 1 more on the fold. The 
sulcus of the pedicle valve originates about 5 mm. anterior to the beak and usu- 
ally occupies from one-half to three-fourths the width at the front; flanks flat- 
tened and with moderately steep slopes. Brachial valve strongly convex in both 
profiles with more or less prominent fold originating anterior to the sulcate 
umbo. Fold gently rounded in profile, moderately elevated above the flanks 
anteriorly ; flanks rounded and with steep slopes. 
Measurements in mm.— 
Brachial 
Length length Width Thickness 
Figured hypotype (III5IO).......... 17.0 15.5 16.4 11.9 
x as (rrrgpyaieiet f Oils 16.8 15.2 17.7 13.6 
s Gimrgoga))i: 62 . cee 15.7 13.7 14.8 11.3 
Types.—Holotype: A.M.N.H. 530/1; figured hypotypes: 111497a, 111509, 
111510, G.S.C. 1040; measured hypotype: 111409. 
Horizon and locality—vValcour formation in New York: Abundant in the 
vicinity of Chazy, Rouses Point (15’) Quadrangle, and on Valcour Island, 
Plattsburg (15’) Quadrangle. 
St. Martin formation in Quebec, Canada: At Montreal. 
Aylmer formation in Canada: In the Ottawa Valley. 
Row Park formation in Pennsylvania: From a cut on Pennsylvania Highway 
995, south of Conococheague Creek, 1 mile north of Welsh Run (identification 
doubtful), Mercersburg (15’) Quadrangle. 
Discussion.—Rostricellula plena is one of the largest and most robust species 
of this genus. It is characterized by a low but wide fold and sulcus, both occu- 
pied by numerous costae. The brachial valve is much deeper than the pedicle 
valve and is strongly swollen and convex. Although this species is one of the 
earliest of the genus, its large size and robust form mark it as an advanced type. 
The only Appalachian species approaching this one in size is R. tumidula. The 
two species, however, are not likely to be confused because R. twmidula is more 
strongly costate, has a more shallow sulcus and lower fold, and somewhat less 
strongly convex valves. 
