“LEPIDOPLEURUS (LEPTOCHITON) AGESILAUS, new species.
Chiton small, with a rounded back and very narrow girdle, the valves white, but coated with a black deposit (manganese ?) which obscures the sculpture; anterior valve nearly semicircular, with almost microscopic radial striation decussated by concentric even finer striae; posterior valve with a moderately prominent mucro slightly in front of the center, the central area finely axially puncto-striate, the posterior area radiatelv striate, the ridges more or less granulose from intersection by concentric striation; intermediate valves with obscure concentrical undulations which make the posterior edge irregularly denticulate; pleural tracts and undifferentiated jugal area axially minutely puncto-striate; girdle minutely densely spinose, the ends of the spinulae forming an arenaceous even surface except at the outer margin which has a short fringe of slightly longer whitish spinules; interior whitish, the jugal sinus obsolete, the sutural laminae small, narrow. Length of animal, 8; width, 5; height, 3 mm. Gills ambient.
Habitat.—Straits of Magellan in 61 fathoms sand, bottom temperature 48° Fahrenheit. United States Fish Commission steamer Albatross. Cat. No. 96227, U.S.N.M.
One of the specimens has only half the seventh valve developed, the vacant space being covered by a widening of the sixth valve on that side.”
(Dall, 1919: 501)
“Leptochiton (L.) medinae (Plate, 1899)
(Fig. 35. Map 37)
Type: ZMHU.
Type locality: Magellan Strait: Harbour of Punta Arenas, 15-19 m.
Lophyropsis imitatrix Thiele, 1893:388, pl. 31:fig. 36, nom. imp.pro imitator (non E. A. Smith, 1881); Thiele, 1909:4.
Lepidopleurus medinae Plate, 1899:82, pl. 5:figs 204-206; Thiele, 1909:4; Carcelles, 1950:47; Leloup, 1956b:13, fig. 2 (bibliography); Dell, 1971:216.
Lepidopleurus (Leptochiton) agesilaus Dall, 1919:501 (lectoype + 1 paralectotype in USNM, 96227, Str. of Magellan, 110 m); Carcellas & Williamson, 1951:243; von Salvini-Plawen, 1968:258; Ferreira, 1979b:162, fig. 28.
Lepidopleurus agesilaus; Boudet, 1945:135; Carcelles, 1950:47; Leloup, 1956b: 12; Castellanos, 1956:466; Dell, 1964a:113.
Description. Animal elongate oval, twice as long as wide, rather elevated (dorsal elevation 0.38), valves evenly rounded, neither carinated nor beaked, lateral areas hardly raised.
Tegmentum of head valve sculptured with numerous (80) radial rows of small, roundish, closely set granules, crossed by many growth marks, becoming stronger towards the outer margin which is semicircular in outline. Intermediate valves short and wide, anterior margin curved inward between the apophyses, posterior margin almost straight, the umbo not swollen, nor protruded. Central areas sculptured with 70 closely set, longitudinal rows of very small roundish to oval granules, weakly pronounced in the jugal area, stronger towards the side margin. Lateral areas only little raised, sculptured with 15 radial rows of similar granules, interrupted by 7-9 concentric growth marks. Anterior and side margins finely crenulated by the slightly projecting series of granules. Tail valve almost semicircular, slightly narrower than head valve, the mucro pointed, not swollen, a little posterior when seen from above, posterior slope almost straight, only weakly concave directly behind the mucro; anterior margin rather straight, finely crenulated. Antemucronal area sculptured like central areas, postmucronal area like head valve.
Articulamentum white, not covering the very porous inside margins of the tegmentum. The underfolded part of the tegmentum posteriorly very wide. Apophyses wide apart, on the intermediate valves sharply triangular and rather strongly marked with 2 or 3 wavy growth marks, on the inside meeting the anterior margin at an angle of 100°-110°. Apophyses of tail valve less projecting, trapezoid. Jugal sinus very wide, rather deep, little concave.
Colour of tegmentum white, the exposed parts of valves often covered with a black crust of foreign deposits, sometimes brownish, especially in the grooves separating the rows of granules.
Girdle rather narrow, brownish, covered with elongate, conical, bluntly pointed, somewhat transparent, not imbricating, flat, white scales, 75 µm long, 27 µm broad, ornamented with 6 fine riblets. Towards the margin the scales become much shorter, the outer ones 36 µm long, also 6-ribbed. Scattered among the scales elongate, somewhat curved, calcareous spines are found, gradually tapering to a blunt point, very finely longitudinally striated, 120 µm long, 12 µm thick. Marginal spicules stout, sharply pointed, 100 µm long, 21 µm thick, the visible side with 4-5 narrow riblets. Ventral scales elongate, bluntly rounded at the top, arranged in closely set radial, imbricating rows. At the base the scales are truncated, the distal half marked with 5 faint riblets. Near the inner margin the scales are short, 36 µm long, towards the outer margin they grow gradually longer, the infra-marginal ones measuring 80 µm × 30 µm.
Radula with a short, thinly bladed central tooth, somewhat narrowing towards the base; first lateral narrow, somewhat curved inwardly, with a small blade; major lateral with a bidentate cusp, the outer denticle smaller; spatulate uncinal slightly curved, with a long, narrow cutting edge.
Gills merobranchial, adanal without interspace, 9-10 ctenidia on both sides.
Length 10 mm, breadth 5 mm.
Distribution. A rather common, sublittoral species on both sides of southern South America, from Lat. 42° south to Cape Horn, mostly in a depth of 15-30 m, though Leloup reported it from 250-300 m (Golfo de Ancud, Chile).
Observations. Of the type only the 8 shell plates are left (ZMHU). They agree in all respects with the specimens collected by the Lund University Chile Expedition, described and illustrated here. A study of the types of L. agesilaus Dall reveals that they are conspecific with L. medinae, as was already supposed by Ferreira (1979b).
L. medinae is closely allied to L. rugatus of the North-Eastern Pacific, but differs markedly in the girdle armature and radula.”
(Kaas & Van Belle, 1985: 80-83)
