Clithon retropictus - Clithon retropictus

Japanese: イシマキガイ(石散貝) - イシマキガイ（英語表記）Clithon retropictus

A rounded snail shell of the Neritidae family that lives in brackish to freshwater areas. The shell is 2.1 cm high, 2.5 cm wide, globose and robust. The coil is low and four stories tall, and the shell surface is covered with a thick, smooth black-brown skin. On top of that there are usually numerous small triangular yellowish-brown spots, one corner of which points toward the shell opening, paired with a black triangular spot that points in the opposite direction. The shell opening is semicircular and the inside is bluish-white. The lid is made of calcareous material, and has a protrusion on the inside at the bottom that fits into the shell and makes it difficult to remove.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

汽水から淡水域にすむまるいアマオブネガイ科の巻貝。殻の高さ2.1cm，太さ2.5cm，球卵形で堅固。巻きは低くて4階，殻表は厚くて滑らかな黒褐色の皮で覆われる。その上に通常小さい三角形状の黄褐斑が多数あって，その1角は殻口のほうへとがっているが，それと対になって黒色の三角形斑があり，これは反対の方向にとがる。殻口は半円形で内面は帯青白色。ふたは石灰質で内側の下のほうに突起があって殻にはまり，とれにくい。

出典　株式会社平凡社世界大百科事典第２版について　情報

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