The inside of a Californian red abalone shell, Haliotis rufescens.

This red abalone was harvested on North California coast in May, 2005. An American quarter dollar coin (24 mm or a little under one inch in width) is included in the picture to provide scale. The picture shows the inside of an abalone shell. Note the 4 respiratory holes on the upper left hand side of the shell as viewed from below. Notice the large relatively rough spot at the center of the shell. It is the large muscle attachment scar.

By Kowloonese from Wikipedia.

This image has currency in it to indicate scale. Using coins for scale is discouraged as it will require people unfamiliar with them to look up the dimensions or guess, both of which defeat the purpose of the object in the first place. Coins can also reinforce a geographical bias, and some coins' designs are copyrighted. Ideally, a photograph should include a ruler with the subject (example) or an added scale marking. SI ("metric") units are the most commonly used worldwide (see meter and centimeter). Images with coins to indicate scale Common coin diameters for reference: U.S. dollar (as of?): 1¢: 19.05 mm, 0.75 in 5¢: 21.21 mm, 0.84 in 10¢: 17.91 mm, 0.71 in 25¢: 24.26 mm, 0.94 in 50¢: 30.61 mm, 1.22 in $1: 26.5 mm, 1.02 in Canadian dollar (as of?): 1¢: 19.05 mm, 0.75 in 5¢: 21.2 mm, 0.83 in 10¢: 18.03 mm, 0.71 in 25¢: 23.88 mm, 0.94 in 50¢: 27.13 mm, 1.07 in $1: 26.5 mm, 1.02 in $2: 28 mm, 1.1 in Pound sterling as of 2021: 1p: 20.32 mm, 0.8 in 2p: 25.91 mm, 1.02 in 5p: 18 mm, 0.71 in 10p: 24.5 mm, 0.96 in 20p: 21.4 mm, 0.84 in 50p: 27.3 mm, 1.07 in £1: 23.03–23.43 mm, 0.91–0.92 in £2: 28.4 mm, 1.12 in Euro as of 2002: 1c: 16.25 mm, 0.64 in 2c: 18.75 mm, 0.74 in 5c: 21.25 mm, 0.84 in 10c: 19.75 mm, 0.78 in 20c: 22.25 mm, 0.88 in 50c: 24.25 mm, 0.95 in €1: 23.25 mm, 0.92 in €2: 25.75 mm, 1.01 in Deutsch ∙ English ∙ español ∙ français ∙ Gaeilge ∙ italiano ∙ Plattdüütsch ∙ português ∙ sicilianu ∙ svenska ∙ suomi ∙ македонски ∙ русский ∙ മലയാളം ∙ 한국어 ∙ 日本語 ∙ 中文 ∙ 中文（简体）‎ ∙ עברית ∙ +/−

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