4-627: Litoceras is a trocholitid (Tarphycerida) genus that has been found in the Lower and Middle Ordovician of Newfoundland . Whorls in Litoceras have a broadly rounded cross section with its width greater than its height. Litoceras somewhat resembles the tarphyceratid Pionoceras from the same time, except for the siphuncle being dorsal and in the center. Species within the genera Litoceras include: Trocholitidae The Trocholitidae are Tarphycerida with whorls in close contact as with
8-550: A dorsal impression. Discoceras and Curtoceras have somewhat subquadrate whorl sections and are moderately impressed. In Graftonoceras and Jasperoceras the venter is rounded and continues smoothly through the flanks to a broad dorsum which in each is moderately impressed. The siphuncle in Graftonoceras is on the dorsal margin, in Jasperoceras it is between the center and dorsum. Whorls in T rocholites have
12-557: A wide cross section and low profile, in Wichitoceras they are laterally compressed resulting in a high-profile. Litoceras has a broad cross section and a deeply impressed dorsum. As with Discoceras and Curtoceras the siphuncle is between the center and dorsum. Arkoceras , Trocholitoceras , and Wichitoceras are limited to the upper Lower Ordovician , along with the enigmatic Beekmanoceras which may or may not belong. Curtoceras , Litoceras , and Hardmanoceras begin in
16-604: The Tarphyceratidae , but in which the siphuncle , similar in structure, becomes dorsal. The Trocholitidae are derived from the Tarphyceratidae, perhaps from different tarphyceratids. Members of the Trocholitidae vary in whorl section and siphuncle position. Most are tightly coiled with the dorsum impressed to some degree. As exceptions Arkoceras and Wichitoceras have their whorls touching but without
#548451