Description. Type Ammonites dispar d'Orbigny, 1841. According to Wright (1996), this genus is involute, with a tall, compressed to subquadrate whorl section and an umbilicus that opens in adults. Primary ribs are rounded, more or less straight, with intercalaries or bifurcations and sometimes small umbilical bullae. Ribs are normally thin in juveniles, becoming thicker in adults (sometimes abruptly), then attenuating or disappearing on the body chamber (macroconchs?) or persisting (microconchs?). In the young, the venter is flat, fastigiate, or rounded, with 1, 2, or 3 tubercles. Later, the ribs tend to cross the venter, thickening as they do so, and the tubercles weaken or disappear. Upper Albian and Lower Cenomanian: Europe, North and East Africa, India, Japan, USA (Texas and Arizona), Brazil and Mexico.
Subgenera. Stoliczkaia sensu stricto from the Upper Albian (Vraconian) has a flat or rounded venter, except in juveniles which display siphonal and ventrolateral tubercles, normally non-persistent. The ribs may taper over the body chamber. Shumarinaia Matsumoto & Inoma, 1975, also from the Upper Albian, is small, somewhat evolute and compressed, with broad and widely spaced ribs, angular or with blunt tubercles on the shoulders, appearing very early. It is unknown in France. Finally, Lamnayella Wright & Kennedy, 1978 (Lower Cenomanian) is of medium size and has a fastigiate venter, weakly trituberculate in juveniles but regularly rounded in adults. The narrow but high ribs are more spaced out than in Stoliczkaia and Shumarinaia.
Three albian species. According to Wright and Kennedy (1978, 1994). S. (S.) notha (Seeley, 1865) is compressed (H/T = 1.18–1.45), involute (O/D = 18.3–23.8%), with parallel flanks. The venter is trituberculate and fastigiate before 20 mm, then the tubercles disappear and the venter becomes rounded. The primary ribs, predominant, are proverse, thin, straight or slightly convex, sometimes curved forward near venter. On the body chamber, which becomes evolute, they swell at the top of the flanks and especially on venter (photographs on the left). S. (S.) dispar (d'Orbigny, 1841) has juveniles without siphonal tubercles. Then, the phragmocone is that of S. (S.) notha but the body chamber is more involute (O/D = 10.7-16.5%), taller (H/T = 1.33-1.61), with more convergent flanks and reduced ornamentation: straight and spaced primary ribs, attenuated on the outer half of the flanks, frame up to four thinner intercalaries (see d'Orbigny's holotype). S. (S.) clavigera (Neumayr, 1875) is descended from S. (S.) notha, but the juvenile has weaker tubercles. It is thicker on average (H/T = 1.07–1.33), with a flattened venter, ribs often concave at the top of the flanks, and a body chamber that remains involute. The ribs also persist on the body chamber but are not as prominent as in S. (S.) notha.