Conus
masasensis (Marks, 1951)
Description of the species (based on holotype and three paratypes.) (1)
Shell small, biconic, spire about one-fourth of height; nucleus elongate, of about
three whorls with apical angle of 28 degrees;
spire of six concave, unadorned, turreted whorls, with pleural angle of about 80° ; body
whorl ornamented on upper half by
rows of small nodes arranged perfectly in spiral lines and crudely along growth lines, on lower half by
about 12 flat-topped, raised bands
slightly wider than their interspaces; shoulder of body whorl obscurely tuberculate; siphonal
notch moderately deep; outer lip
strongly retractive; anal notch deep; anal fasciole concave. Variations in pleural angle, which
ranges from 75 to 85 degrees; in nodes
of body whorl, which may be isolated or on raised bands; in number of bands of nodes, which
ranges from five to seven.
Dimensions. — Holotype, length 16.3 mm., diameter
8.3 mm.
The largest of four specimens from the type locality, paratype no. 20496, has a diameter of
8.7 mm.
The most characteristic features of C.
masasensis are the noded upper half of the body whorl with the accompanying obscurely tuberculate
shoulder on the body whorl only,
and the elongate nucleus.
Conus masasensis is placed in Leptoconus
because of its strongly retractive
outer lip, deep anal notch, and shallow siphonal notch. It is related to both the Conus (Leptoconus) multiliratus Bose group and to Conus (Leptoconus) sophus Olsson. Members
of the species C. multiliratus
differ from C. masasensis in being broader and having a shorter nucleus.
The subspecies C. multiliratus spiekeri Olsson from the
Lower Miocene Lower Zorritos formation of northwestern
Peru is noded like C. masasensis, but differs from C. masasensis in the character
of the nodes as well as in shape and
nucleus. C. sophus from the Lower Zorritos formation of Peru is not noded, but in all other
respects, including size and character of
nucleus, closely resembles C. masasensis.
A common ancestry may exist. Conus berryi Spieker from
the Lower Zorritos formation of
Peru is somewhat similar to C. masasensis in general appearance and size; however, it is not noded on
the body whorl, and bears tubercles
on the latter spire whorl shoulders.
Conus
(Leptoconus) imitator lius Woodring of the Bowden
Miocene is also similar to C.
masasensis, but lacks the nodes and is larger.
Conus (Leptoconus) masasensis occurs in the
Lower Miocene Subibaja
formation in the northeastern part of the Progreso Basin. The detailed stratigraphy of this
sector has not been worked out, and
its position within the formation is not known. Associated with C. masasensis
is a large assemblage of mollusks including
Conus (Leptoconus) roigi, Nuculana
(Adrana) sp., Natica sp.,
etc. The enclosing strata are siltstone or fine silty sandstone. The trivial
name masasensis is taken from the village of Las Masas, which is close to outcrops from
which the type specimens were
taken.
Material. — Holotype no. 20495, Paleontological
Research Institution, from locality LP.C. 2558, 3.0 km. N 56° W of the village
of Las Masas, Guayas
Province, Ecuador. Paratype no. 20496 (figured) from the same locality.
Paratypes no. 7990 (two specimens) in
the Stanford Univ. Paleont. coll. from the same locality.
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Conus masasensis Lower Miocene Subibaja fm. Las Masas - Ecuador |
Conus masasensis |
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Conus masasensis |
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Conus
masasensis Plate 8 fig. 9,10 |
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Bibliografia Consultata
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(1) - Marks, J. G., 1951. Miocene
Stratigraphy and Paleontology of Southwestern Ecuador. Bulletins of American
Paleontology, 23 (139 ).
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