Vinlandostrophia acutilirata

• Three nearly equally developed plications in the sulcus
• Ventricose, with about thirty two sharp very prominent ribs
• Hinge extremity winged and acute
• Inferior mesial fold very profound
• Cardinal area moderate, profoundly impressed or obliquely inclined

• Articulate brachiopod. Characterized by three nearly equally developed plications in the sulcus, by the numerous plications (ten or more) on each side of the sulcus, and by the low, rounded fold. Whitewater.

McFarland (1931):

• Typical P. acutilirata is a strongly ventricose shell, characterized by a low, broad, rounded fold with four approximately equal plications, and numerous plications along the convex lateral slopes. There is every variation in hinge line from long, with spine-like cardinal extremities, to shorter than greatest width. The following varieties have been recognized:
  var. prolongata – forms with spine-like cardinal extremities. The typical form of P. acutilirata has the very extended hinge and acute cardinal angles, but not spinelike; and var. senex – a gerontic form with greatly thickened shell, thickness often in excess of length and a tendency toward the more rectangular cardinal angle.

McEwen (1919):

• This species is spiriferoid, much extended on the hinge. The brachial (dorsal) valve is strongly ventricose; the slopes are inflated to such a degree that the fold rises but slightly above the general convexity. The pedicle (ventral) valve is less convex than the brachial (dorsal) valve. The slopes are compressed and the inner edges are elevated. This gives a thin appearance to the shell near the cardinal angles and adds to the depth of the conspicuous sinus. There are four plications on the fold and three on the sinus which are of about equal strength. The slopes are occupied by about 13 or more closely spaced plications. The cardinal areas of both valves are strong and broad. The beaks are strongly incurved.
• This species has conspicuous gerontic characters. The convexity is so great that it may equal or exceed the heigth. The shell is thickened centrally and anteriorly to such a degree that the space occupied by the soft parts is exceedingly small when compared with the size of the shell. Both valves are marked by strong growth lines which in the early ephebic stage run out to the cardinal extremes and are closely spaced.
• Mr. Conrad reported the Silurian of the Falls of Ohio as the locality from which his types were collected. Mr. Meek recognized that his figures were in agreement with specimens from Richmond, Indiana. Mr. S.S. Lyon, of Jeffersonville, Indiana, who was familiar with the paleontology of that locality, reported that he had never found such a shell in that area. Mr. Meek sent the Richmond specimens to Mr. Conrad and he identified them as the same as he had figured under the name Delthyris acutilirata.
• Measurements. 35.5 mm along the hinge line, 27 mm wide across the middle, 18.2 mm high, 20.8 mm thick, 13.3 mm sinal width, 11 mm sinal depth, 4 mm fold height.
• Occurrence. Richmond group: Whitewater formation: Richmond, etc., Indiana; Oxford and Dayton, Ohio; North Carolina and Louisville R.R. between Wauhatchie and Hooker, Tennessee. Fernvale limestone: Savannah and Wilmington, Illinois. Maquoketa shale: Delafield, Wisconsin.
• Plesiotypes. Cat. No. 48606, U.S.N.M.

Cumings (1907):

• I have pointed out an exactly similar case in the variety sense of Platystrophia acutilirata (16). This variety occurs in the upper part of the Whitewater division of the Richmond series of Indiana and Ohio. Platystrophia acutilirata, as is well known, is very mucronate in the adult, resembling in its general outline, Spirifer mucronatus. It was in fact at first referred to the genus Delthyris (Spirifer). The normal form is shown by an unusually closely graded series of intermediate forms to be descended from P. laticosta, and it repeats the adult characteristics of the latter very faithfully in its late neanic stage, becoming always more mucronate as development proceeds.

Foerste (1903):

• Platystrophia acutilirata is a descendant of Platystrophia laticosta. The typical specimens of Platystrophia laticosta begin their appearance in the Bellevue bed, and thence continue through the remainder of the Lorraine stage into the Lower Richmond. In the Lower Richmond a part of the specimens show an increase in the number of lateral plications and a prolongation of the poster-lateral angles, features which find their most pronounces expression in Platystrophia acutilirata.

Conrad (1842):

• Delthyris acutilirata Ventricose, with about thirty two sharp, very prominent ribs, and four larger costae on the mesial fold of the upper valve, which is elevated, flattened at the sides, and convex on the back; hinge extremity winged and acute; inferior mesial fold very profound; beaks nearly equally prominent; cardinal area moderate, widest on the inferior valve, profoundly impressed or obliquely inclined.

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