PLATE L. 
I, 2, 3, 4. Spirifer Trigonalis. ( Trigonal Spirifer.) Gibbose ; cardinal area acute at extremities ; umbones 
incurved, approximate ; upper valve semi-circular, rounded, with longitudinal, divergent ribs ; lower valve flat, 
with fine, transverse striae. 
5. S. Triangularis. {Triangular Spirifer.) Elongated, triangular, convex ; cardinal area flat; front eleva¬ 
tion acute ; mesial fold narrow; with smooth, longitudinal ribs. 
6, 7. S. Lineatus. {Lineated Spirifer.) Gibbose; umbones produced, remote; cardinal area long, narrow, 
with triangular foramen; front semi-circular; mesial fold elevated, ending in beak; with many, granulated 
striae. 
8. S. Beanii. {Bean's Spirifer.) Beaks approximate; cardinal area contracted; hinge-line parallel; with 
strong, radiating sulci; mesial fold broad, smoothish. 
9, 10. S. Octoplicatus. {Eight-plaited Spirifer.) Elongated, semi-circular, inflated ; beaks remote ; cardinal 
area wide, triangular, with eight to ten, angular, longitudinal plaits ; with crenulated margin ; mesial fold plain. 
II, 12. S. Pinguis. {Plump Spirifer.) Gibbose, globular, obovate; beaks close; cardinal area shallow, 
with eight or nine, longitudinal ribs on each side of mesial fold. 
13, 14. S. Walcottii. {Walcott's Spirifer.) Sub-orbicular, gibbose, smooth; cardinal area triangular; both 
beaks with angular foramen ; mesial fold wide, with four, longitudinal ribs on each side. 
15, 16. S. Minimus. {Least Spirifer.) Oblong, inflated, smooth ; umbones acute at points ; cardinal area 
long, flat; with fifteen, longitudinal ridges. 
17, 18. S. Rotundatus. {Rounded Spirifer.) Globose, obovate ; cardinal area triangular; beaks incurved; 
upper valve with smooth ridge; with depressed, longitudinal ribs, crossed by lines of growth ; margin of valves 
sharp. 
19, 20. S. Striatus. {Striated Spirifer.) Elongated, sub-compressed ; cardinal area wide, smooth, acute at 
sides; mesial sinus angular ; beaks incurved; with many, longitudinal ribs and lines of growth. 
21,22. S. Bisulcatus. {Two-furrowed Spirifer.) Gibbous, semi-circular; cardinal area long, with parallel 
sides; beaks prominent, curved, with deep sulcus on each side of mesial ridge; with about thirty longitudinal 
ribs. 
23, 24. S. Semi-circularis. {Semi-circular Spirifer.) Upper valve semi-circular; cardinal area sharp at 
extremities ; beaks obtuse ; mesial fold broad, sulcated ; with radiating, longitudinal ribs. 
25, 26. S. Attenuatus. {Attenuated Spirifer.) Convex, elongated ; cardinal area straight, with parallel 
edges ; sides produced, acute ; beaks short; front rounded; mesial fold, with deep sulcus on each side ; with 
many, linear sulci. 
27, 28. S. Undulatus. ( Waved Spirifer.) Convex, elongated; cardinal area flat, narrow, with parallel 
edges ; beaks approximate ; mesial elevation inflated ; with many, longitudinal ribs, crossed by regular striae. 
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