''Knefastia waltonia'' is an extinct

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

, a marine

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Pseudomelatomidae Pseudomelatomidae is a family of predatory sea snails, marine gastropods included in the superfamily Conoidea (previously Conacea) and part of the Neogastropoda ( Bouchet & Rocroi, 2005). In 1995 Kantor elevated the subfamily Pseudomelatomina ...

, the turrids and allies.

Description

The length of the shell attains 38 mm, its diameter 11.4 mm. (Original description) The shell is of moderate size for the genus, fusiform, with the maximum diameter in front of the median horizontal. The

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

is approximately half the total altitude. The shell contains about 11

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

s. The

protoconch A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called ...

is small but rather high, twice coiled. The initial turn is erect, submerged only at the extreme tip and slightly bulbous. The succeeding volution is high, increasingly compressed laterally. The line of demarcation between the conch and the protoconch is defined by the initiation of a faint peripheral ridge a little in front of the median line of the whorl, a ridge which becomes increasingly prominent and near the end of the first whorl of the conch is defined by a faint sulcus and threadlet behind it. A feeble spiral is also introduced near the end of the first whorl directly behind the anterior suture line and within half a turn, another directly in front of the posterior suture, neither one of them attaining any prominence. The adult whorls are bicarinate, the spiral directly behind the periphery increasing in strength until it is almost or quite as elevated as the peripheral keel, from which it is separated by a rather narrow, concave interspiral area. This is sculptured with protractive incrementals and in places a fortuitous spiral threadlet. The area between the suture and the posterior keel is strongly concave, sculptured with 2 faint spirals, both of them introduced near the beginning of the conch, the one a little in front of the suture, the other at an equal distance behind the posterior carina, and between them a smoothly concave interspace striated with strongly and symmetrically arcuate incrementals and a few very faint spiral lirae. Microscopic spirals are also present directly in front of the posterior suture and on the concave space between the anterior keel and the anterior suture. Two additional primaries are shown equal in prominence and spacing to the carinal spirals, upon the body, and about 12 similar primaries, regularly spaced and gradually decreasing in size anteriorly, upon the very base of the body and the columella. Secondaries are intercalated on the columella, in some specimens as many as 3 between a single pair of primaries, and a very fine threading upon the fasciole. The suture line is distinct but inconspicuous, overhung by the periphery. The

is pyriform, abruptly expanding posteriorly. The siphonal notch is placed midway between the posterior carina and the suture line, U-shaped, with parallel sides, the anterior limb more produced than the posterior. The parietal wall is thinly glazed. The anterior canal is long, very slightly curved, with proximate parallel margins.Gardner J.A. (1937). The molluscan fauna of the Alum Bluff Group of Florida. Part VI. Pteropoda, Opisthobranchia and Ctenobranchia (in part). United States Geological Survey Professional Paper. 142-F: 251-435, pls 37-48
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Distribution

This extinct marine species was found in

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

strata in the Alum Bluff Formation of Florida, USA.

References

waltonia Gastropods described in 1937 Miocene gastropods {{paleo-Pseudomelatomidae-stub