Description. Type species Turrilites bergeri Brongniart, 1822. This genus belongs to the family Turrilitidae, composed of helicoid heteromorph ammonites. It is defined by a conical shell with contiguous whorls, a more or less circular whorl section, and simple, oblique, sometimes weak ribs bearing four tubercles. The tubercles of successive ribs form four spiral rows. The siphuncle follows the upper margin of the whorls. The suture is deeply incised. Cosmopolitan genus found from the Late Albian to the Early Cenomanian: Europe, North Africa, South Africa, Madagascar, Iran, India, New Zealand, Texas, Mexico, and Argentina (Spath, 1937; Wright, 1996).
Subgenera. The subgenus Mariella sensu stricto has four more or less equidistant spiral rows of tubercles and a rounded whorl section. Its age and geographic distribution are those of the genus. The subgenus Winstonia Adkins, 1928, is distinguished by a spiral groove between the second and third rows of tubercles and by an uncoiled body chamber. It is found in California, Texas, Mexico, southern India, and Madagascar.
A few species. The type species M. (M.) bergeri (Brongniart, 1822), with 19 to 30 tubercles per whorl, is common in the Upper Albian (left, photograph by Jattiot et al., 2022, with row 4 below the last whorl). It is found alongside M. (M.) miliaris (Pictet & Campiche, 1861), which has finer ornamentation and 33 to 40 tubercles per whorl, and M. (M.) crassicostata Spath, 1937, which has about twenty strong tubercles. M. (M.) cenomanensis (Schlüter, 1876), common in Europe in the Lower Cenomanian, lacks distinct ribs. Its uppermost row of tubercles is located rather low. A wide, smooth band separates this row from the following ones.
Remarks. Several species of Mariella are illustrated in the following references: Atabekian (1985), Latil (1995), Wright & Kennedy (1996), Matsumoto (1999a, 1999b), and Jattiot et al. (2022). Some Turrilites with 3 or 4 rows of tubercles have an external appearance very similar to Mariella. The presence of a fourth row must be confirmed by looking under the last whorl. If we know that the specimen is albian, there is no possibility of confusion, since the genus Turrilites is Cenomanian.