26 
PALEONTOLOGY OF NEW-YORK. 
UNIVALVES ( GASTEROPODA ) OF THE CHAZY LIMESTONE: 
Plates V., V. (bis), & VI. 
46. 3. MACLUREA MAGNA. 
Pl. V. Figs. 1 a, b, c, d; and Pl. V. (bis). Figs. 1 a, b, c. 
Maclurites magna. Leseuer-, Jour. Aead; Nat. Sci. Philad., Vol. i. pag. 312, pl. 13, figs. 1, 2, 3. 
Mac/urea. Emmons, Geol. Report, pag. 276, fig. 1. 
Sinistrorsal, discoidal, depressed-turbinate ; breadth more than twice as great as the 
height; spire flat, a slightly depressed line at the sutures ; whorls about six, gradually 
increasing from the apex, ventricose, flattened above, obtusely angular on the outer edge; 
surface marked by fine striae, which, upon close examination, are found to be produced by 
the imbricating edges of lamellae ; striae undulating, bending backwards from the suture, 
and forwards in passing over the edge of the shell ; aperture obtusely trigonal, depressed 
above, slightly expanded beyond the dimensions of the whorl just behind it; axis hollow ; 
umbilicus broad and deep, extending to the top of the spire. 
Plate V. 
Fig. 1. The upper surface partially denuded of the shell, showing the striae with the smooth cast beneath. 
This is a perfect representation of the shell, except that the minute terminal volution is 
not shown. 
Fig. I a. Side view of a cast of. the shell, showing the depressed turbinate form and flat spire. 
Fig. 1 b. View of the lower surface, somewhat worn, showing the large umbilicus, which is partially 
filled with stony matter. 
Fig. 1 c. A vertical section of the shell, near, but not directly through the centre of the spire, showing 
several volutions and the deep umbilicus. Such sections of the shell are not unusual in 
the rock, and they are generally vertical to the lines of deposition. 
Fig. 1 d. A view of the shell worn down from the lower side, as it very commonly appears upon the 
weathered surfaces of the rock at Chazy. 
i Platf. V. (bis). 
Fig. 1 a. An obliquely vertical section of the fossil, passing nearly through the centre of the spire above, 
but more on one side below, so as to escape the umbilicus. 
Fig. 1 b. A vertical section of the outer volution. A common appearance upon the weathered surface of 
the rock at Chazy. 
Fig. 1 c. An unusually large specimen of the same species; the surface worn so as to obliterate the strise, 
and obscure the first volutions. 
\ 
This shell is. exceedingly abundant in the limestone at Chazy and some other places. 
Sections of the shell in every possible position are seen, covering the weathered surfaces 
and forming a large part of several strata, and less abundant in some others. In the black 
