Makylaxd Geological Survey 475 



aperture broad, campaiiulate; margin deeply sinuate. Surface marked by 

 fine concentric or transverse lamellose stride, and stronger wrinkles or 

 folds. The striae are abruptly bent backwards on the upper dorsal side, 

 and a deep sinus marks the labrum : tlie lower side of the aperture is like- 

 wise deeply sinuate." Hall, 1859. 



Occurrence. — Oriskany Formation, Eidgely Member. East side 

 Nicholas Mountain. 



Collection. — Maryland Geological Survey. 



[Ohern.] 



Platyceras trilobatum Hall ? 

 Plate LXXXIY, Figs. 7, 8 



Platyceras trilobatum Hall, 1859, Nat. Hist. N. Y., Pal., vol. iii, p. 316, pi. Ivii, 

 figs. 5a, 6, c, 1861. 



Description. — " Body of the shell obliquely or arcualely ovoid, trilobate : 

 volutions three or four, the last one (or more) becoming free, gradually 

 expanding to the aperture ; the apex closely involved and rising above the 

 plane of the outer volution, or sometimes on the same plane, concave 

 towards the suture : aperture subangularly ovate, sinuate on the right and. 

 left sides, and the shell extended in front. Surface marked by two strong 

 spiral depressions corresponding to the sinuosities of the aperture, and 

 crossed by lamellose stris which are strongly undulated on the sinuosities 

 of the last volution, and are marked by other undulations on the earlier 

 volutions, indicating former sinuosities in the margin of the aperture." 

 Hall, 1859. 



A specimen in the U. S. National ]\Iuseum is much smaller than those 

 figured by Hall, but in other respects closely resembling this species. The 

 three sinuses are shown better by the undulating stri^ on the surface than 

 by the aperture. It is referred, with hesitancy, to this species ; the absence 

 of the spire making identification uncertain. 



Occurrence. — Heldehbekg Formation, New Scotland Member. 

 Corriganville. 



Collection. — U. S. National Museum. 



[Ohern.] 



