348 PALAEONTOLOGY OF NEW-YORK. 



is closed by the columella a little within the base. In the Gait specimen, fig. 1 a, 6, the shell 

 is preserved on the lower half of the last volution only. 



Fig. 1 a, b. Two views of a specimen of this shell. 



Fig. 1 c. A small individual. 



Fig. 1 d. An impression of the base of this shell in limestone. 



Position and locality. Fig. 1 a, b, d, are from the limestone at Gait, Canada West ; fig. 

 1 c is from the Onondaga-salt group, Newark, Wayne county, N. Y. 



716. 22. PLEUROTOMARIA BISPIRALIS (n. sp.). 



Pl. JLXXXIV. Fig. 2 a, b. 



Volutions about four or five, rapidly increasing from the apex, subangular, and marked above 

 and on one side by thin sharp carinse or spiral elevated lines. 



This species is extremely rare, a single mould of the exterior only having been found. 



Fig. 2 a. A cast from the mould fig. 2 b. 



Fig. 2 6. A mould of this species, showing four volutions. 



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



717. 23. PLEUROTOMARIA? sp. 



Pl. LXXXIV. Fig. 3. 



Cast composed of two or three volutions, which expand rapidly from the apex ; the maiks 

 of a strong double carina are preserved on the last volution j aperture much expanded. 



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



718. 24. PLEUROTOMARIA SOLARIOIDES («. sp.). 



Pl. LXXXIV. Fig. i a, b. 



Spire depressed, composed of about five volutions which are externally rounded ; lateral 

 diameter of volutions greater than the vertical: base discoid, flattened; umbilicus broad, 

 reaching to the apex. 



This species is about the size of P. lenticularis of the lower silurian rocks, but it is readily 

 distinguished by its rounded volutions. 



Fig. 4 a. The base of a specimen, showing the umbilicus. The outline of the shell is obscured 



by the adhesion of the surrounding stone. 

 Fig. 4 b. The upper surface of an imperfect specimen. 



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



