ONONDAGA-SALT GROUP. 



345 



GASTEROPODA. 

 708. 19. MURCHISONIA BIVITTATA (n. sp.). 



Pl. LXXXIII. Fig. 1 a, b. 



Spire elongated ; volutions numerous (more than twelve), rounded, a little flattened in the 

 cast, very gradually increasing from the apex ; aperture unknown ; surface unknown ; columella 

 marked by a double spiral fold or carina. 



I refer this species to the Genus Murchisonia, without having been able to verify the cha- 

 racters of the surface. The specimens examined are all casts, with the single exception of fig. 

 1 b, which shows the interior of the shell and the broken edges of a longitudinal section. The 

 succeeding species is marked by a carina below the centre of the volution, as shown in a mould 

 of the shell, indicating its relations with Murchisonia. The present species, of similar form and 

 general characters, I have therefore referred to that genus. The very gradual increase in the 

 size of the volutions is one of the striking characters of the species, though exceeded in the 

 following one. 



Fig. 1 a. A cast of six volutions from the central part of the shell. There were originally about fire 



or six above the highest one shown in the figure. 

 Fig. 1 J. A longitudinal section of several volutions, showing the columella, marked by a double 



spiral fold, and the edges of the broken shell. 



Position and locality. In the limestone at Gait, Canada West, 



709. 20. MURCHISONIA LONGISPIRA (n. sp.). 



Pl. LXXXIII. Fig. 2 a, b. 



Spire extremely elongated and very slender ; volutions numerous, rounded on the surface 

 and carinated below the centre ; surface unknown. 



The mould of one specimen of this species shows impressions of a carina below the centre 

 of the volution, but the impressions of striae are not preserved. In the fragment fig. 2 6, nine- 

 teen volutions are visible ; and in a mould of the same species, I have counted twenty-five, and 

 the base still imperfect. The columella is proportionally larger than in the preceding species, 

 and shows no fold or carina. The slender spire and more numerous volutions are sufficient to 

 distinguish this one from all the other species of the rock, and indeed from any species known 

 in our strata. 



Fig. 2 a. A mould of the middle part of the spire, preserving a portion of the shell and columella 



near the base. 

 Fig. 2 6. A fragment showing in the upper part the cast of the interior; the lower part of the 



specimen preserves the shell, which is divided longitudinally. 



Position and locality. In the limestone at Gait, Canada West. 



