﻿30 Bulletin 20 108 



figures. The smallest specimen measures 4 mm. in width and 

 4.3^ mm. in length. This shell shows no trace of the fold and 

 sinus characterizing the mature shells. A slightly larger speci- 

 men shows the fold and sinus barely perceptible beyond the 

 anterior margin of the shell, where they are distinctly marked. 



Locality. — Princeton, Montana. 



Athyris montanensis n. sp. 

 PI. Ill figs. 3 - 3 b. 



Shell small, subcircular in outline. Dorsal and ventral valves 

 moderately and about equally convex. A broad fold and sinus 

 are developed near the front of the shell, but are obsolete a short 

 distance posterior to the front. The sinus is a slightly convex 

 broad low and depressed ridge in the anterior half of the 

 value. Two or three low, broadly rounded but rather in- 

 distinct plications are discernible on either side the fold and 

 sinus at the margin of the shell, but obsolete a very slight distance 

 from the front. 



The broad sinus, slightly concave in the middle, distinguishes 

 the species from Athyris vitata and its varieties, with which it 

 seems closely allied in other respects. 



The species is represented by two specimens of almost pre- 

 cisely the same size, having a length and breadth of 7 mm. and 

 maximum thickness of 5X mm. 



Locality. — Princeton, Montana. 



Spirifer occidentalis n. sp. 

 PI. Ill figs. 4 - 4 d. 



Shell small, plano-convex, subcircular in outline. Hinge line 

 rounded at the extremities. 



Ventral valve convex, very gibbous and elevated in the 

 umbonal region. Beak obtuse and closely incurved over the 

 small delthyrium. Area small and inconspicuous. A broad, 

 shallow sinus in anterior third of shell terminates in a tonguelike 

 extension corresponding to fold in dorsal valve. Sinus flanked 

 by low rounded ridges at the front. Both ridges and sinus are 

 obsolete in posterior two-thirds of valve. Indications of a second 

 plication on either side the sinus are seen at the front of the 



