PLATE LXXI. 
1. MytilllS Edentulus. {Toothless Mytilus.) Elongated; beak sharp; disc obtusely carinated; 
posterior side straight; front rounded, obtuse; surface smooth; hinge without teeth. 
2. M. Lanceolatus. {Spear-shaped Mytilus.) Lanceolate, curved, smooth ; beaks acute; disc 
carinated, smooth; within each beak a lamellate tooth. 
3. 4. Dreissina Brardii. {Brard’s Dreissina.) Convex, straight, fusiform, elongated; beaks 
acute; within each a transverse plate for the tendon; valves arcuated. 
5,6. M. Inaequivalvis. {Unequal-valved Mytilus.) Sub-triangular; beaks central, broad, sub¬ 
compressed ; surface smooth, with faint, concentric lines of growth. 
7, 8. M. Tridens. {Three-toothed Mytilus.) Elongated, convex, carinated; beaks acute; hinge¬ 
line straight, with three unequal teeth; surface very smooth. 
9, 10. M. Prselongus. {Lengthened Mytilus.) Elongated, narrow, arcuated, carinated; hinge¬ 
line straight, long, without teeth ; surface smooth ; shell very thick. 
11. M. Edlllis. {Edible Mytilus.) Obovate; beak acuminated, curved, smooth; hinge, with 
three teeth ; side deeply indented. 
12,13. Modiola Funata. {Buried Modiola.) Transversely oblong-ovate; hinge-line arcuated; 
beaks very blunt; surface, with wrinkled lines of growth. 
14. M. CuneatllS. {Wedge-shaped Mytilus.) Cuneiform, short; posterior side straight; anterior 
side produced; beaks obtuse; surface smooth, with widish striae. 
15. M. .ffiquilatus. {Equal-sided Mytilus.) Oblong-oval, sub-compressed ; sides broad, equal; 
hinge-line straight; beaks obtuse, central; surface smooth, with remote, ill-defined lines of growth. 
16. M. Affinis. {Allied Mytilus.) Obliquely elongated; sides parallel, straight; anterior margin 
reflected; arcuated ; surface smooth, without teeth. 
17. M. Antiquorum. {Ancient Mytilus.) Oblong-ovate, gibbose; beaks obtuse ; hinge, with 
three or four, slight teeth; surface smooth. 
18. M. PeetinatUS. {Pectinated Mytilus.) Rather quadrangular, slightly arcuated; oblong, 
gibbose; beaks produced; surface with deep, regular stria?; two, obtuse angles emanating from base 
of valves. 
19. Pinna Ampla. {Spacious Pinna.) Triangular, compressed; posterior side straight; base 
curved ; surface, with widish, longitudinal, undulating stria?; posterior side not striated; shell thin. 
20. Perna Alseformis. {Wing-shaped Perna.) Triangular, with wing-like appearance; ventri- 
cose; anterior lobe compressed; posterior lobe minute; back parallel, disc convex ; beaks produced; 
surface rough, imbricated. 
21. Modiola Latissima. {Very Broad Modiola.) Transverselyeiongated; compressed; anterior 
side curved, produced; posterior side small, ill-defined; beaks short, obtuse; surface almost smooth, 
with a few, irregular lines of growth. 
22. 23. M. Bipartita. {Two-parted Modiola.) Transversely elongated; gibbose, smooth; 
anterior side obtuse; posterior lobe irregular; beak sub-carinated ; front waved. 
24, 25. M. Williamsoni. {Williamson’s Modiola.) Transversely elongated, narrow, compressed; 
anterior side short; posterior side elongated; umbones depressed, blunt; surface, with wrinkled 
lines of growth. 
26. M. Sublaevis. {Half-smooth Mytilus.) Oblong, triangular, arcuated; beaks acute; disc 
carinated; front straight; hinge-line parallel; surface, with strongish lines of growth. 
27. M. Lyellii. {Lyell's Mytilus.) Oblong-ovate; flattened; narrowed above, expanded below; 
beaks sharp, beneath which valves inflated. 
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