Species: longus MARSH, 1878
Etymology:

Holotype: YPM 1920 (USNM 2672; skull)

Locality: Marsh-Felch’s YPM Quarry 1, Garden Park, Sec. 28, T17S, R70W, Canyon City, Fremont County, Colorado.

Horizon: Salt Wash Member, Morrison Formation.

Biostratigraphy: Zone 2.

Age: Comobluffian age, Kimmeridgian Stage, uppermost Malm Epoch, Late Jurassic.

Referred material:

BLUMBERG & SOKOLOFF, 1961

CM 84, AMNH 223, AMNH 493, AMNH 608: Coalescenced caudal vertebrae.

CM 94: 17-18, 22-23 caudals fused.

USNM 10865: 17-18, 19-23 caudals fused.

AMNH 655: 18-21 caudals fused.

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Species: hallorum (GILLETTE, 1991) (emend OLSHEVSKY, 1998)
Etymology: In honor of the late Reverend James W. Hall, former director of the Ghost Ranch Conference Center, Abiquiu, New Mexico, and his wife Ruth, honoring their support of paleontology in northern New Mexico spanning three decades.
= Seismosaurus halli GILLETTE, 1991

Holotype: NMMNH 3690

Locality: Seismosaurus Quarry, 16 km west of San Ysidro, Bernalillo County, Central New Mexico.

Horizon: Upper Brushy Basin Member, Morrison Formation.

Biostratigraphy: Zone 3.

Age: Upper Part, Comobluffian age, Kimmeridgian Stage, uppermost Malm Epoch, Late Jurassic.

Material: One isolated and seven articulated dorsal vertebrae, articulated ribs, both ilia and ischia, one pubis, sacrum, caudal vertebrae 1-8, 12-16, and 20-27, five chevrons, with 230 gastroliths.
Note: LUCAS, 2000, LUCAS, HECKERT, HUNT & SULLIVAN,2004 do not believe that these are gastroliths but are actually stream-deposited pebbles.
Note: Pathologic distal expansion on the ischium,LUCAS, HECKERT, HUNT & SULLIVAN,2004.