90 



fourth septum, 20 lines ; lateral, 21 lines. Grimsby ; Niagara formation. 

 J. Pettit. 



This species is closely allied to iS. Janus, but diflfers in having the 

 aperture proportionally Avider on the lateral diameter, and in the outline 

 of the body of the shell on the dorsal aspect — straight or concave instead 

 of convex. The two species are closely allied, and may yet be united 

 by intermediate forms. 



Fig. 28. 



F. 28. — The upper figure represents the aperture of *S'. Janus in 

 outline : the lower figure the aperture of *S'. Heros. 



CYSTIDE^. 

 Genus, Apiocystites, Forbes. 



A. Canadensis, n. sp. — Small, ovate, sub-pentagonal, rounded at the 

 summit, truncated at the base. Arms five, four of them extending 

 downwards to within one-fifth of the whole length from the base ; the 

 fifth a little shorter than the others. Mouth ? a little above the mid- 

 length, apparently closed by numerous small plates. The two upper 



