Conus triangularis

Conus triangularis (Finlay, 1924)

Conus trigonicus (Tomlin, 1937)

Description.

Shell small, apparently rather thin and fragile. Protoconch lost in both specimens seen, but apparently projecting above perfectly flat spire. Whorls at least 6, with linear sutures hardly distinguishable from sculpture-lines, horizontal above, but acutely keeled at periphery of body-whorl, forming an almost perfect angle of 65°, then rapidly sloping to canal, but slightly indented in two places—just below keel and a little above canal. Spire-whorls, and that part of body-whorl above keel, bear 4 strong spiral cords, of which inner and outer are wider and flatter than middle pair; the rest of body-whorl covered over whole surface with rather strong and closely-set spiral cords, low and rounded, a little less than their own width apart. Aperture filled with hard matrix, but evidently very narrow; columella twisted in front. Posterior sinus, as indicated by lines of growth, is apparently extremely shallow, and removed from suture.

Holotype: height, 16 mm.; width, 15 mm.

Paratype has the corresponding dimensions 17 × 16½ mm.

Type and one paratype, from Kakanui (on the beach near the quarry, from tuffs below the limestone), in author's collection.

This is the second representative of Lithoconus that has been found in New Zealand.

Conus (Lithoconus) abruptus Marshall occurs at Pakaurangi Point, but the Kakanui shell is not related to it except subgenerically, differing in its squat shape, much more acute keel, and totally different sculpture.

Here, again, the nearest ally is Australian, Conus (Lithoconus) dennanti Tate, of Balcombian and Janjukian beds, and these two are very closely allied. The crown of C. dennanti is a little concave, that of the New Zealand shell almost perfectly plane. Harris (Cat. Tert. Moll., pt. 1, p. 33) comments on the sharpness of the keel of C. dennanti; that of our shell is sharper still and the angle somewhat smaller. The Australian shell is rather elongate (33 × 20 mm.), approaching more the shape of C. abruptus Marshall (20 × 11 mm.), the ratios of height to width being:

Conus abruptus Marshall = 1·82;

Conus dennanti Tate = 1·65;

Conus triangularis Finlay n. sp. = 1·07.

The sculpture, keel, and spire of C. dennanti Tate, however, remove it from the vicinity of C. abruptus Marshall, but indicate its very close relationship to C. triangularis Finlay n. sp., the differences being in degree alone.

Conus trigonicus (Tomlin, 1937)

Conus trigonicus Tomlin 1937, p. 206: new name for C. triangularis Finlay, preoccupied by Conus berghausi triangularis (Sacco, 1893)

Description: Rather small for family (height 16-25 mm), conical, spire flat or very depressed. Protoconch riot known. Teleoconch of about 6 whorls, periphery sharply angled, sides of last whorl straight or slightly concave. Sculpture of low, narrow spiral cords present over whole surface in some shells, but absent from parts of the last whorl on others. Aperture narrow, inner and outer lips parallel.

Comparison: Conus trigonicus is readily distinguished from other New Zealand cones by its very depressed or even flat spire, its relatively broad shape and its relatively prominent spiral sculpture. C.abruptus (Otaian-Altonian, Pakaurangi) also has a very depressed spire, but it is more slender than C. trigonicus and has far less prominent and less ubiquitous spiral sculpture. As Finlay (1924b, p. 479) pointed out, C. trigonicus seems to be most closely related to C. dennanti Tate, 1892 (mid-Cenozoic, Victoria).

Cone shells are among the most characteristic molluscs of present-day tropical or subtropical seas, although a few species are present in cooler waters (e.g. Victoria; northern New Zealand). The earliest definite New Zealand record of the family is from the Bortonian (Hampden Beach); at least three species are known from the Kaiatan and Runangan, but there are very few records from the Landon Series (see Pl. 15k, n). Cones are relatively common and diverse from Otaian to Clifdenian and rather less so from Lillburnian to Kapitean. Thereafter the family almost completely disappears from the fossil record, presumably because of late Cenozoic cooling. C. trigonicus seems to be a member of the low-spired species group that has been shown in several recent papers to constitute the genus Conus sensu stricto (Duda & Kohn 2005; Bandyopadhyay et al. 2008; Puillandre et al. 2008).

Distribution: Kaiatan (A stage in the Lower Tertiary of New Zealand, underlain by the Bortonian, overlain by the Runangan, and roughly contemporaneous with the Bartonian Stage, Upper Eocene); type supposedly from "tuffs below the limestone", Kakanui, but almost certainly from the Waiareka Volcanic Formation, Lorne, where this species occurs rarely (Maxwell 1968).


Conus triangularis ⁽²⁾ Pl. 48 fig. 10a, 10b mm. 16 x 15 Kaiatan - Kakanui

Conus trigonicus M.026954 Museum of New Zealand Te Papa Tongarewa 55 Cable Street PO Box 467 Wellington, 6011 New Zealand Phone: +64 (04) 381 7000

Conus visagenus (Kilburn, 1974)

Comparison between the Conus trigonicus and the Conus visagenus is particularly interesting: although millions of years have passed and they are thousands of kilometers away, the correlation between C. triangularis ad C. visagenus, a species that inhabits depths of more than 100 meters, is undeniable