Original Description of Perissoptera (Hemichenopus) thomsoni by Allan, 1926:
- " Six early whorls and a worn featureless protoconch are preserved. Whorls rapidly increasing in size. Older whorls almost straight, slightly concave above, slightly convex below, ornamented with close even spiral cords about 20 per whorl, interstices of same width with very fine spirals; keel obsolete. Earlier whorls becoming strongly keeled immediately above well-marked suture. Keel ornamented with oblique nodules which become more prominent towards protoconch. Spiral cords crossed by oblique curved growth-lines. Spire-angle 40º. Length of first six whorls 22 mm: width of sixth whorl, 13 mm."
Locus typicus: Waihao Downs, Canterbury, South Island, New Zealand
Stratum typicum: Waihao Greensand, Bartonian, Eocene
Perissoptera (Hemichenopus) thomsoni in Allen, 1926, pl. 76, fig 1, Copyright Royal Society of New Zealand / National Library of New Zealand