12 



valve pointed, straight, with a triangular foramen. Surface 

 marked by fine concentric striae, and some faint remains of 

 finer radiating striae. 



Length, '22, width '24 of an inch. 



Locality. — Alton, 111. 



ORTHIS, Dalman. 



Orthis dubia. — Shell circular, or oval-ovate ; valves nearly 

 equally convex, the ventral valve somewhat more rotund ; 

 dorsal valve flattened in the middle, with a broad depression 

 extending thence to the front of the shell, giving it a sinu- 

 ous outline ; beak of dorsal valve extended beyond the op- 

 posite valve, slightly incurved, with a triangular foramen ; 

 area very small, and (with the foramen of the dorsal valve) 

 nearly covered by the beak of the ventral valve, which 

 curves towards the opposite valve bringing the two almost 

 in contact at their margins. Surface marked by fine round- 

 ed, closely arranged striae, which increase by bifuication and 

 implantation ; the striae down the mesial depression are dis- 

 tinctly tubular, with minute, pore-like openings at intervals, 

 directed downwards. These are probably the bases of mi- 

 nute tubular spines which were closely imbricated. Minute 

 pore-like openings are sometimes seen on other parts of the 

 shell, but never so conspicuous as in the dorsal sinus. 



Length, *09 to '45, width *10 to *45 of an inch. 



Locality. — Spergen Hill ; Bloomington, la. ; Alton, 111. 



It is possible that this species will prove to be the young 

 of 0. Michilina. 



Orthis umbraculum, Schlot. — There are several small 

 specimens in the collection which appear to be identical with 

 0. umbraculum. The specimens are scarcely more than half 

 an inch in diameter. 



Locality. — Spergen Hill, Bloomington. 



PRODUCTUS, Sow. 

 , Productus biseriatus.— Shell longitudinally ovate ; dorsal 



