The genus Ontaria Clarke, 1904 includes a group of small, almost circular bivalves that occur abundantly in the Mid- and Late Devonian pelagic facies. These bivalves are characterised by their straight hinge line, small and, central beak, as well as commarginal rugae (if present). Based on an extensive review of type material and additional samples as well as a comprehensive literature review, this study identifies three valid species Ontaria suborbicularis Hall, Ontaria concentrica von Buch, and Ontaria iniquistriata Beushausen. Thirteen Ontaria species are either not valid or have been synonymised, and three species that were previously included in Ontaria do not belong to this genus. Representatives of Ontaria first occur in the late Eifelian and become abundant in the Frasnian and Famennian. Ontaria last occurs in the late Famennian before the Devonian/Carboniferous boundary. This genus has been identified as a representative of the family Cardiolidae previously reported only from the Silurian, making Ontaria the first report of a Devonian cardiolid taxon. Ontaria inhabited low-energy, generally well-oxygenated, off-shore environments. The overall shell morphology, small size, and the presence of a small siphon supports the idea that Ontaria lived semi-infaunal in/on muddy substrates.

Ontaria Clarke属，1904 年包括一群小的、几乎是圆形的双壳类动物，它们大量出现在泥盆纪中晚期的远洋相中。这些双壳类动物的特点是它们的铰链线直、小而中央的喙，以及边缘皱襞（如果有的话）。基于对类型材料和其他样本的广泛审查以及全面的文献审查，本研究确定了三个有效物种Ontaria suborbicularis Hall、Ontaria concentrica von Buch 和Ontaria iniquistriata Beushausen。安大略省的13 个物种无效或已被同义，以及先前包含在安大略省的三个物种不属于这个属。Ontaria 的代表首先出现在埃菲尔阶晚期，并在弗拉斯阶和法门阶变得丰富。安大略最后出现在泥盆纪/石炭纪边界之前的晚法门纪。该属已被确定为先前仅从志留纪报告的心形科的代表，使安大略成为泥盆纪心形分类群的第一份报告。安大略省居住在低能量、一般充氧良好的近海环境中。整体壳形态，尺寸小，和一个小虹吸管的存在支持了Ontaria住半infaunal中/上泥泞基材。