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| A. Ribs, about 50, lightly built, shape elongate subquadrate. | strangi |
| B. Ribs, about 38, heavily built. | |
| I. Rib interstices narrow to linear, shape subquadrate. | gudexi |
| II. Rib interstices broad, shape elongate subquadrate | spatiosum |
| C. Ribs, about 41 | oneroaense |
Maoricardium strangi (Laws).
1930. Cardium strangi Laws, Trans. N.Z. Inst., 61: 549, figs. 6, 9.
Locality: Shell Gully, Kelly's Farm, Chatton.
Age: Duntroonian.
A second specimen, a left valve, now in the Geological Survey Collection, has been collected at the type locality by Mr Axel A. Olssen, Mr E. O. Macpherson, and the writer. This specimen is somewhat more attenuated than the holotype.
Maoricardium gudexi (Laws). (Pl. 37, Fig. 29.)
1933. Cardium gudexi Laws, Trans. N.Z. Inst., 63: 316, figs. 7, 14.
Localities: Sutherlands, South Canterbury (type); shell bed above upper limestone, lower gorge of Porter River, Trelissick Basin.
The Trelissick specimen has well developed tubercles like oneroaense, but the radials are flat. See remarks under oneroaense.
Maoricardium oneroaense (Powell).
1938. Cardium oneroaense Pow., T.R.S.N.Z., 08: 307, pl. 38, figs. 7–8.
The type of oneroaense has a few more ribs than the type of gudexi, and they are slightly more convex, the anterior tubercles are better developed, also the shell is lighter built, so that the hinge is less arched. These differences are little, if any, greater than those to be seen between individuals of M. spatiosum, and since the matrix of oneroaense is more argillaceous than that of gudexi, the differences may be due to habitat. As in the case of H. greyi and cantuariense, the true relationship of these forms can only be determined from a larger number of specimens than now available.
Locality: Oneroa, Waiheke Island.
Age: About Awamoan.
Maoricardium spatiosum (Hutton). (Pl. 37, Fig. 30.)
1873. Cardium spatiosum Hutt., Cat. Tert. Moll. 23.
1914. Suter, Pal. Bull. 2: 52, pl. 15, figs. la, b.
Localities: Waitotara (type) the precise locality has. not been determined: M. spatiosum occurs widely in Waitotaran beds and was obtained by Laws (1940, p. 37) from beds considered to be low in the Nukumaruan. This appears to be an exceptional occurrence, however, for the species is not known from the Nukumaruan else-where. Maoricardium is known from Opoitian and Taranakian beds
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at several places and has generally been recorded as spatiosum. No good specimens, however, have yet been seen from beds between Awamoan and Waitotaran, so where the boundary should be drawn between spatiosum and gudexi is not known.