Bittiinae Cossmann, 1906

Subfamily Bittiinae Cossmann, 1906 View in CoL

Diagnosis. “ Shell small, turreted, narrowly elongate to pupate, with moderate spiral and axial sculpture frequently cancellate and/or beaded. Aperture with short but distinct anterior canal. Spiral sculpture usually 4-5 spiral cords per whorl.” ( Houbrick 1993: 269).

Discussion. There is presently no known diagnostic feature of shell morphology or internal anatomy that allows unambiguous placement in Cerithiinae versus Bittiinae ( Strong & Bouchet 2013, 2018). Therefore, the placement of fossil species in Bittiinae is to some extent subjective. Herein we place species in this subfamily based on their resemblance to extant congeners.

Genus Argyropeza Melvill & Standen, 1901

Type species. Argyropeza divina Melvill & Standen, 1901 View in CoL ; by monotypy ( Melvill & Standen, 1901: 371). Present day, Indo-West Pacific (IWP) Region.

Diagnosis. “ Shell small, 6-8 mm in length, thin and vitreous, turreted and with 9-12 whorls sculptured with weak axial riblets and with two spiral cords bearing sharp nodules where crossed by axial riblets. Sinusigera protoconch of about three and a half whorls, sculptured with two spiral lirae and spiral band of pustules adjacent to suture. Tip of protoconch smooth, domeshaped, white, remainder chestnut in color. Protoconch sculpture sharply separated from adult sculpture of teleoconch. Former varices present on shell, with prominent varix opposite outer lip of aperture. Suture deeply impressed, set off with inferior and superior sutural ramps. Aperture ovate with short but distinct anterior siphonal canal and weak anal canal. Outer lip thin, columella concave.” ( Houbrick 1980).

Discussion. All Argyropeza species have small, thin shells with randomly placed varices with the most prominent one being opposite the outer lip. All species have distinct anal canals and deeply impressed sutures with sloping ramps. The sculpture consists of weak axial ribs and more prominent spiral cords with small, sharp tubercles ( Houbrick 1980). Fossils of the genus have been known so far only from the Pliocene of the IWP Region ( Houbrick 1980). According to Houbrick (1980), all fossils represent Argyropeza divina Melvill & Standen, 1901 , reported from Japan ( MacNeil 1961), the Philippines ( Shuto 1969) and Java ( Martin 1884, as Cerithium spinigerum Martin, 1884 ). Thus, the herein described Argyropeza spina ( Hörnes, 1855) is the stratigraphically oldest record pushing the origin of the genus back to the Middle Miocene. Moreover, it documents a Western Tethyan occurrence of this genus, which is now restricted to the IWP Region. Argyropeza species differ from Bittium species in having two primary spiral cords on teleoconch whorls as opposed to three or more, a more distinct anal canal, and a protoconch with two strong spiral cords, which are weak in Bittium species if present.