The Atoll of Funafuti, Ellice group : its zoology, botany, ethnology and general structure based on collections made by Charles Hedley of the Australian Museum, Sydney, N.S.W.
Triforis obesula, Jousseaume, — (Fig. 31)
Triforis obesula, Jousseaume,
Jousseaume, Bull. Soc. Mal. France, 1884, p. 255, pl. iv. fig. 17; Tryon, Man. Conch., ix., 1887, p. 185, pl. xxxviii., fig. 27.
Jousseaume's account of this species is not accessible to me and I have to assume that Tryon gives a faithful transcript of it. That however only allows me to identify the shell I now figure and describe as T. obesula, with probability rather than certainty. My perplexity is increased by the fact that the Funafuti shell is identical with specimens received from New Caledonia labelled "T. limosa, Jousseaume," with the description of which they disagree in shape and size.
The species is distinguished by its small size, corpulent shape and dark brown (burnt umber) hue. The type of sculpture differs from that of the other species of Triforis from Funafuti. The gemmules are so closely packed within the row and are so page 445feebly divided from one another, that they seem rather to be a continuous keel, like that of T. corrugatus, in process of breaking down into beads. The earlier adult whorls are ornamented by two bead-rows. Between them there arises in the antipenultimate a thread, which gradually increasing becomes a full grown row in the last whorl; the addition of a median and two basal rows brings the number of rows on the last whorl to six. Tryon states that the "three anterior ones are unarmed," but all are beaded in the example before me.
The anal notch is simple and comparatively shallow. The protoconch has five whorls, the first hemispherical and smooth the others bicarinate and obliquely crossed by rather coarse bars which do not bead the carinae. The adult sculpture suddenly commences in the sixth whorl with a row of small beads above and a large gemmed ridge below. The latter is remarkable in several specimens before me for its white colour, giving the shell to the unaided vision a distinct white collar beneath the acicular apex. Tryon gives the length as 8 mm. Of the examples before me the New Caledonian measure 4½, the Papuan 4, and the decollated shells from Funafuti 3½ mm.
Two decollated specimens occurred to me in the Funafuti lagoon. I have also taken the species between tide marks in Port Moresby, British New Guinea. A Papuan specimen supplied the material for the above account of the apex, missing in Funafuti and New Caledonian examples.