31. "Karagandoceras " has an involute , lenticular shell, with an acute ventral margin. 32. The "'base cylinder "'corresponds to the involute tooth surfaces are developed. 33. A few genera are more involute , with successive whorls partially embracing the flanks of the previous. 34. The left-handed involute of an all-fifths tuning is an all-fourths tuning. 35. For oil cooling the engine has an involute heat exchanger or a shell and tube heat exchanger. 36. "' Spur gear teeth "'are manufactured by either involute profile or cycloidal profile. 37. The shell of " Albanites " is more or less involute , smooth or faintly ribbed. 38. "Anapachydiscus " has a rather involute shell with a broad to moderately compressed whorl section. 39. The same involute gear may be used under conditions that change its operating pitch diameter and pressure angle. 40. Shells are variable in form, both ribbed, evolute forms and smooth, involute forms are included.
