. Bulletin of the British Museum (Natural History), Geology. . Fig. 5. Diagrammatic representations of the different styles of ornament in the genus Trematis : "a "â âradial rows of pits ; " b "âradial rows of pits separated by radial ribs ; " c "âpits arranged in quincunx ; " d "âpits arranged hexagonally. Superfamily DISCINACEA Gray Family TREMATIDAE Schuchert Genus TREMATIS Sharpe, 1848 The most distinctive features of this genus are the large pedicle notch of the ventral valve and the unusual ornament. The latter is commonly described as consisting o
. Bulletin of the British Museum (Natural History), Geology. . Fig. 5. Diagrammatic representations of the different styles of ornament in the genus Trematis : "a "â âradial rows of pits ; " b "âradial rows of pits separated by radial ribs ; " c "âpits arranged in quincunx ; " d "âpits arranged hexagonally. Superfamily DISCINACEA Gray Family TREMATIDAE Schuchert Genus TREMATIS Sharpe, 1848 The most distinctive features of this genus are the large pedicle notch of the ventral valve and the unusual ornament. The latter is commonly described as consisting of " small pittings . . arranged either in quincunx or in radiating rows " (Hall & Clarke, 1892 : 139) ; further distinctions are made on the shape of the pits, and in the second case, on the presence or absence of radial ribs between the rows. A review of the species ascribed to the genus leads the present writer to the conclu- sion that there are four basic types of ornament within the genus as understood at present. These are shown diagrammatically in Text-fig. 5. In style " a " the pits are arranged radially but are not separated by ribs as in " b ". Style " c " shows a. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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