100 PALEONTOLOGY OF NEW YORK. 



SPECIES OF THE HAMILTON GROUP. 

 Bellerophon PATULUS. 



PLATE XXII, KIGS. 17-30; AND XXIV, FIGS. 3-8. 



Bellerophon patulus. Hall. Geology of N. V. Surv. Fourth Geol. Dist., p. 196, fig. 1. 1843. 



•• « " Descriptions of New Species of Fossils, etc., p. 29. 1861. 



•• » " Fifteenth Rep. N. Y. State Cab. Nat. Hist., p. 57. 1862. 



B. (Phragmnttomat) patulus. Hall. Illustrations of Devonian Fossils : Gasteropoda, plate 23. 1876. 



Shell subglobose, ventricose ; umbilicus small, closed before reaching the 

 centre. Volutions rounded, the last one abruptly and widely dilated, 

 giving a broad subcircular aperture, the width greater than the dorso- 

 ventral diameter. The lip is somewhat flattened and repand towards the 

 exterior margin and broadly sinuate in front, contracted and more or less 

 thickened at the postero-lateral margins, nearly inclosing and partially 

 overlapping the volution on the posterior side, and extending more or less 

 entirely over the columellar lip in a thickened callus, the exterior por- 

 tion of which is pustulose. Inner margin of the columellar lip thickened 

 and smooth, sometimes truncate, but usually projecting in a prominent 

 boss in the centre. 



Surface, on the expanded part of the outer volution, marked by fine, close, 

 concentric striae, which are sometimes crowded in fascicles, giving an 

 undulating surface ; the posterior prominent part of the volution is 

 marked on the back, and partially on the sides, by strong, even, arching 

 costae, which are more abruptly and sometimes subangularly curved on 

 the dorsal line. These costs) sometimes continue for half the length of 

 the volution anteriorly, gradually becoming obsolete on the middle and 

 sides, and are never seen upon the broad expansion of the shell. The 

 spaces between these costae are marked by fine, close, concentric striae, 

 and, in well-preserved specimens, extremely fine revolving striae are 

 sometimes visible. The costaB become finer or obsolete as they approach 

 the umbilicus, and the surface is marked only by the fine striae of growth. 



