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. 

Bibliografia Consultata

·         (1) - Marks, J. G., 1951. Miocene Stratigraphy and Paleontology of Southwestern Ecuador. Bulletins of American Paleontology, 23 (139 ).

·