27© 
PALAEONTOLOGY OF NEW-YORK. 
Cyrtina liamiltoiiensis, var. recta. 
PLATS' 5LIV. 
Figures 36 an d37 of Plate xyii illustrate tliis form, which has a plane 
flat area, without incurvation of the beak, and with angular plications. 
This form is not uncommon in the Hamilton group, and was for a long time the 
only one known to me in the Chemung group ; hut very recently I have received, 
among a collection of Spirifera disjuncta from the southern part of the State, 
a specimen which indicates that the species may have in this horizon the same 
variations which it has in the formation below. 
Cyrtina curvilineata [ ? ] 
PLATE XLIV. 
Compare Cyrtia curvilineata, White : Proceedings of the Boston Society of Nat. History, Vol.ix, p. 25. 
Shell rather large, obliquely subpyramidal : hinge-line equalling or 
slightly less than the greatest width of the shell; length of dorsal 
valve less than its width, and one-third greater than the height of 
area of the ventral valve. Entire surface plicate. 
Ventral valve obliquely subquadrilateral in outline, the apex turned to 
the left : area much elevated, inclined backwards, slightly incurved. 
The fissure has apparently been closed in the lower part, but the 
pseudo-deltidium is broken away, and there is no evidence that the 
upper iwo-thirds of the fissure has been closed at any recent period of 
the animal’s life. 
Dorsal valve semielliptical, convex in the middle and flattened at the 
cardinal margins; mesial fold prominent towards the front. 
Surface marked by about twelve or thirteen rounded plications on either 
side of the mesial fold and sinus. The mesial fold has four or five low 
rounded plications near the front, while there are four corresponding 
folds on the sinus. 
This species has the general form and proportions of the C. liamiltonensis , and 
occurs with that species in rocks of the age of the Hamilton group in the west. 
It differs slightly in some of its proportions from the prevailing eastern forms of 
that species, but not more than is observed among specimens of the same in col¬ 
lections from New-York, Canada West, and the Western States. The distinguishing- 
feature is in the presence of plications on the mesial fold and sinus. The presence 
