Plejona Bolten, 1798.

Suter correctly perceived the affinities of his Athleta necopinata, although his material was exceedingly poor. Fine specimens collected by Mr. R. S. Allan at the type locality show, however, that important differences make it impossible satisfactorily to class this species under either Athleta or Plejona. From Athleta it differs in having one strong anterior fold and several weak posterior ones, all oblique and situated on a pad in the adult; in having a spur on the outer lip opposite the upper row of spines; and in the different disposition of the parietal callus-pad. The columella of immature specimens is like that of Plejona, but in the adult the folds are situated on a thick pad of callus, and the outer lip is thickened, reflexed, and crenulated. From both it differs in having a double row of spines on the whorls, as in Neoathleta, but it is distinguished from all these by the deep anterior notch to the aperture, forming a well-defined fasciole much stronger than that of Athleta. Consequently a new generic division is required, and Notoplejona is proposed, with Athleta necopinata Suter as type.

Suter's recognition of the subgenus Volutocorbis was probably due to Zittel's comparison of his species V. gracilicostata (1864, p. 39) with V. abyssicola Ad. & Rve., a Recent shell which was placed under Volutocorbis by Dall. The New Zealand shell in question is, however, not a Volute, but belongs to a common Tertiary group of Turrids for which the new genus Austrotoma has been proposed by Finlay (1924, p. 515). The relationship of V. gracilicostata to this group was also noticed several years ago by the late Mr. R. Murdoch.

The shell described by Suter (1917, p. 19) under the name of Galeodes maoriana does not belong to that genus, but is a Volute. Indeed, Suter himself (1915, p. 32) classed a specimen of it from Kakahu, the type locality, as Volutospina (Athleta) huttoni var. pseudorarispina. The resemblance to Athleta rarispina Lamk is due to parallelism. The tendency of the body-whorl to embrace preceding whorls and to develop thick callus at the suture is quite a common gerontism in several widely-separated families—e.g., Cominella carinata (Hutton), Uber percrassus (Finlay), Baryspira robusta (Marwick).

The apex of “Galeodes” maoriana has not been completely preserved in any of the available specimens. The protoconch was certainly quite small, but there is no direct evidence as to whether it was scaphelloid or not. On the first conch-whorls the angulation was probably well above the suture, but no specimens show this clearly. Fig. 2a shows a specimen in which part of the shell-substance has been removed. The neanic shell is almost biconic, with a flat or slightly concave sloping shoulder, the angle armed with strong tubercles, which extend axially well down on the convex, quickly contracting body. On about the third whorl the suture follows the line of these tubercles, which soon become shorter, so that the shell now represents the adult stage of “Fulgoraria” biconica Suter. For perhaps a quarter-volution the tubercles are obsolete and the shell is almost regularly rounded, but the suture meanwhile has been climbing slightly above the periphery, so that when the tubercles again become stronger they are well below the line of suture. On the body-whorl a thick callus is