OEISKAHT FAUNA OF BECRAFT MOUNTAW 45 



ing the genus. Particularly well developed is tlie broad, flabellate 

 muscular scar of the pedicle-valve and the median septum of the bra- 

 chial valve, extending for more than half the length of the shell. 



The brachial valve resembles in its less extreme conditions that of 

 the associated specimens of M. lata, but the shell taken in its entirety- 

 can not be confounded with any other species. 



Meristella lata Hall 



1859. Meristella lata Hall, Paleontology of New York. 3 : 431, pi. 101, fig. 

 3, a-in 



1892. Meristella of. laevis Clarke, op. cit. p, 414 



The specimens which represent this species are of very much smaller 

 size than the forms of this Oriskany shell which have been described, 

 but they show no wide departure therefrom in other respects. 



Meristella (?) vascularia, sp. nov 



Plate 6, fig. 13-14 



Among these fossils are frequently found internal casts of large 

 pedicle-valves of an elongate Meristella- like form with broad median 

 sinus developed over the anterior region. Notwithstanding that these 

 specimens are not uncommon, I have not been satisfied of the charac- 

 ter of the brachial valve to be referred to them, nor has it been 

 possible to get a very clear conception of the exterior of the shells. 

 These interior casts differ from that usual to Meristella in the 

 following respects. Very prominent dental lamellae are developed by 

 convergence and union into a strong spoon-shaped process, which fills 

 the umbonal region and rests on the bottom of the valve, its anterior 

 edge being free. The corresponding structure found in the Meris- 

 tellas is of diminutive size compared with this. In front of this 

 process lies the elongate, often obscure central nuiscular scar, which in 

 Meristella is much more strongly developed and constitutes the 

 most conspicuous feature of the interior. From the mai-gins of the 

 spondylium, even traversing the central scar, diverge strong radial grooves 

 which cover the umbonal and median regions of the valve, disappearing 

 about the margins. These features are uniform in all specimens, though 

 the vascular lines are less conspicuous in young sheEs. 



