26 PAUEONTOLOOY OF NEW-YORK. 



UNIVALVES {GASTEROPODA) OF THE CHAZY LIMESTONE 

 Plates V., V. (bis), & VI.. 



46. 3. MACLUREA MAGNA. 



Pl. V. Figs. 1 a, b, e, d; and Pi« V. (bis). Figs. 1 o, b, e. 



Machtritei magna. Lescuer, Jour. Acad. Nat. Sci. Philad., Vol. i. pag. 312, pi. 13, figs. 1, 2, 3. 

 Maclurea. Emmons, Geol. Report, pag. 276, fig. 1. 



Sinistrorsal, discoidal, depressed-turbinate ; breadth more than twice as great as the 

 height ; spire flat, a slightJy 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 stria with the smooth cast beneath. 



This is a perfect representation of the shell, except that the minute terminal volution is 



not shown. 

 Fig. 1 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 «. 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. 



Plate 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. I 6. A vertical section of the outer volution. A common appearance upon the weathered surface of 



the rock at Chazy. 

 Fig. 1 c An imusualiy large specimen of the same species; the surface worn so as to obliterate the striaB, 



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 



