174 PALEOZOIC PALEONTOLOGY. 
it is not a member of the recent genus Chiton. It is subpentagonal 
in outline, obtusely angular in front, its posterior margin slightly 
sinuate. Along the median line it is quite sharply rounded toward 
the apex, but becomes more broadly rounded posteriorly, with a sight, 
longitudinal, median groove, becoming stronger posteriorly. The sides 
slope down to the lateral margins with a gentle convexity. The sur- 
face is smooth. 
Its dimensions are: length, 7 mm.; breadth, 7 mm. 
GASTROPODA. 
ARCHINACELLA PATELLIFORMIS (Hall). 
Plate XII., Figs. 1-2. 
1847. Carinaropsis patelliiformis Hall, Pal N. Y., vol. L, p. 183, pl. 
40, figs. 2a—b. 
Description.—Shell subovate in outline, slightly narrowed posteri- 
orly, patelliform, obliquely depressed, conical, obtusely subcarinate 
along the median, dorsal line; the apex situated anteriorly, slightly 
incurved and extended in a line with or a little beyond the margin. 
Surface marked by fine, concentric lines of growth. 
The dimensions of a nearly-perfect specimen are: length, 11 mm. ; 
breadth, 9 mm.; convexity, 4 mm. 
CYRTOLITES ORNATUS var. MINOR U. & S. 
Plate XII., Figs. 6-7. 
1897. Cyrtolites ornatus var. minor U. & S., Pal. Minn., pt. IT., p. 
861, pl. 62, figs. 30-31. 
Description.—Shell small, usually not exceeding 10 mm. in di- 
ameter. Volutions two or three, rapidly imcreasing in size, strongly 
and sharply carinate dorsally, rhombic-subquadrate in section; sides 
prominent and subangular or narrowly rounded along a line about 
three-fifths of the height of the volution within the dorsal carina, 
