Hystrivasum Olsson & Petit 1964

Genus Hystrivasum Olsson & Petit, 1964

Type species. Vasum horridum Heilprin, 1887; by original designation. Pleistocene, Florida.

Diagnosis. Shell large, solid, up to 135 mm in length, biconic; sculpture consisting of one or two peripheral rows of spines, a row of subsutural spines, three or four spiral rows of spines at base of last whorl, and four or five high scaly cords on central sector of shell whose scales or short spines are oriented adaperturally; umbilicus open; outer lip relatively thin, glazed at edge but not on abapertural side; outer lip smooth on inner side; columella with three or four folds, the adapical-most fold widest and highest; posterior-most row of basal spines emerge adapically to posterior-most columellar fold; siphonal canal long, straight.

Included species. Hystrivasum barkleyae Petuch, 1994, Early Pliocene; H. chilesi Petuch, 1994, Early Pleistocene; H. griffini Petuch, 1994, Early Pleistocene; H. hertweckorum Petuch, 1994, Late Pliocene; H. horridum (Heilprin, 1887), Early Pleistocene; H. hyshugari Petuch, 1994, Late Pliocene; H. jacksonense (Vokes 1966), Early Pliocene; H. kissimeense Hollister 1971, Late Pliocene; H. lindae Petuch, 1994, Late Pliocene; H. locklini (Olsson & Harbison, 1953), Late Pliocene; H. olssoni (Vokes, 1966), Pliocene; H. palmerae Hollister, 1971, Late Pliocene; H. schrinerae Hollister, 1971, Early Pleistocene; H. squamosum Hollister, 1971, Early Pleistocene; H. violetae Petuch, 1994, Late Pliocene; H. vokesae Hollister, 1971, Late Pliocene; all from Florida.

Material examined. Hystrivasum horridum: CAS Caloosahatchee Formation;Vermeij collection Caloosahatchee Formation, Miami Canal; H. barkieyae: Vermeij collection, Early Pliocene, Sarasota. H. locklini: CAS, Ortona Locks, Glades County; Vermeij collection, Pinecrest Member, Tamiaml Formation, Sarasota. H. olssoni: CAS, lower Pinecrest Member, Tamiami Formation, Sarasota; Vermeij collection, same locality.

Remarks. Hystrivasum is a distinctive Early Pliocene to Early Pleistocene genus from Florida. Its distinguishing features include prominent subsutural spines, high spiral cords bearing adaperturally directed scales on central sector of shell, three or four rows of short spines on base of last whorl, and adapical-most row of basal spines emerging posterior to posterior-most columellar fold. The umbilicus is open and the inner side of the outer lip is smooth. The genus shares with other American vasids a narrowly glazed adult outer lip and an open umbilicus. Vokes (1966) suggested that Hystrivasum is derived from a form similar to her Vasum chipolense (here assigned to Aristovasum), but that species has a flaring posterior end of the aperture that is unlike the polished adapical subsutural spine seen in Hystrivasum.