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1. Introduction.
The Volutes constitute one of the most beautiful and varied groups of the Mollusca, and include some of the rarest shells. As a result they have long attracted the attention of conchologists, and many subdivisions have been proposed with a view to their more accurate classification.
The modern study of the family dates from Dall's revision of 1890. His paper, though concerned principally with the Tertiary of Florida, covered much general ground, and proposed as a new major classification of the Volutidae two series which were later called subfamilies. This division was based on researches made by Dall into the manner of growth of the animals in their early stages, and was as follows:—
| A. |
Volutoid series. Protoconch calcareous from the earliest stage.
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| B. |
Scaphelloid series. Protoconch at first horny. *
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[Footnote] * “In the typical form the larva is clothed with a cutiqular or horny protoconch probably similar in form to that which when shelly results in the bulbous nucleus of the other line of descent. Later on, but while still in the ovicapsule, the deposition of limy matter begins as a slender cone or elevated point along the line of the axis of the protoconch, and as the larva grows the posterior part of the mantle secretes a shelly dome.” The horny protoconch, being thus cut off, disintegrates, and the apex of the shell “presents a slightly irregular dome, with a slender point rising from the apical part…. In some other forms the elevated point is almost or entirely wanting”; and in a third group “the nucleus is enormous but apparently secondary to a protoconch.”—(Dall, 1890, pp. 67, 68.)
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Cossmann (1899) criticized this method of relying on the nature of the protoconch alone for fundamental divisions, and proposed six subfamilies—Volutinae, Homoeoplocinae, Cymbinae, Zidoninae, Volutobulbinae, and Loxoplocinae—based on the sum of the shell-characters.
These proposals were not followed by Dall in his Revision of the American Volutidae (1907), where he used the subfamily divisions Volutinae and Caricellinae (Scaphella had been dropped, for reasons shown below). In a recent paper on the value of nuclear characters (1924) he has given reasons for discounting the importance which he and many others formerly attached to the protoconch as a means of classification. This does not, however, preclude its use for a particular family, and in the Volutidae nuclear characters when considered broadly seem to possess considerable significance. In New Zealand, at all events, the nuclei are remarkably constant in shells which agree closely in other characters. As might be expected, there are considerable differences in detail of the scars left by the horny protoconchs, caused by slight differences in the actual time at which the calcareous matter began to be deposited. But, apart from this, the general nature of the nucleus is a valuable guide to the systematic position of the shell.
The Volutidae of New Zealand belong almost wholly to Dall's Caricellinae, the only exceptions being Notoplejona (two species) and Lyria (one species). There is no trace of the large trochoid shelly nucleus belonging to the typical Voluta (V. musica Linné), Amoria (V. undulata Lamk.), and Cymbiola (V. vespertilio Linné). These are common along the east coast of Australia, and extend to New Guinea, Solomon Islands, and New Caledonia; but they do not seem to have reached any farther east.