Revised descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990)
(Pl. 13d): GS10837, I40/f001, head of Lake Waitaki, Duntroonian (GNS)
(Pl. 13e): GS10837, I40/f001, head of Lake Waitaki, Duntroonian (GNS)
Beu & Maxwell (1990): Chapter 10; p. 148; pl. 13 d, e.
Synonymy: Cardium (Trachycardium) waitakiense Suter 1907a, p. 209
Type species of Hedecardium Marwick, 1944
Classification: Cardiidae: Protocardiinae
Description: Size moderate for family (height 60-70 mm), rather thin- shelled, subquadrate, strongly inflated. Posterior area well defined; junction of posterior and posterodorsal margins sharply angled in right valve, more rounded in left. Lunule only weakly differentiated. Radial sculpture on "main" part of shell (i.e. other than posterior area) of 40-48 flat-topped or narrowly rounded costae, interspaces wider than costae on adult. Commarginal sculpture of fine growth ridges in intercostal spaces. Posterior area glossy, with 14-16 subdued, rounded costae that become obsolete towards dorsal margin. Hinge narrow, almost straight, both valves with prominent, pointed anterior and posterior lateral teeth. Left cardinal teeth separate, anterior tooth peg-like, posterior one much smaller. Right cardinals fused dorsally, anterior one the smaller. Adductor muscle scars oval, subequal. Ventral margin crenulate, posterior margin less prominently than elsewhere.
Comparison: Hedecardium olssoni (Duntroonian, Shell Gully, Chatton) is probably conspecific with H. waitakiense it differs only in having fewer (37) radial costae on the main part of the shell, and in having costae of triangular rather than rounded or flattened cross-section.
Hedecardium is an endemic genus first recorded from beds of probable Mangaorapan or Porangan age (H. collinsi; Otaio Gorge, Pareora Gorge) and is probably derived from a Paleocene or Early Eocene species of Nemocardium (sensu lato). The Eocene species are similar in shape and sculpture to H. waitakiense, but are much smaller; H. collinsi is only 21 mm long and H. brunneri (Bortonian-Kaiatan, widespread) is 35-50 mm in length. Hedecardium (sensu stricto) is not known after the Waitakian, but the subgenus H. (Titanocardium) persisted until the Waiauan or Tongaporutuan (see Pl. 19d, e). The genus seems to have been confined to shallow waters (inner or middle shelf).
Distribution: Duntroonian; Wharekuri Greensand, Waitaki River, opposite Wharekuri (type); head of Lake Waitaki; Wendon Valley; Otorohanga; Okoko.
Cite this publication as: "A.G. Beu and J.I. Raine (2009). Revised
descriptions of New Zealand Cenozoic Mollusca from Beu and Maxwell (1990). GNS
Science miscellaneous series no. 27."
© GNS Science, 2009
(Included with a PDF facsimile file copy of New Zealand Geological Survey Paleontological Bulletin 58 in CD version from: Publications Officer, GNS Science, P.O. Box 30368 Lower Hutt, New Zealand)