Genus: Microcleidus WATSON, 1911
Etymology: Greek, mikros, “small” and Greek, kleid- (kleis), “key, clavicle” + us: Small clavicle.
= Hydrorion GROßMANN, 2007
Etymology: Greek, hydro, "water" and Orion, the hunter of Greek mythology.
= Occitanosaurus BARDET, GODEFROIT & SCIAU, 1999
Etymology: From the area where the Occitian language is spoken, currently includes most of southern France, Val D’Aran of Spain and several Pidemont valleys of Italy and Greek, sauros, "lizard": Occitian lizard.

Species: homalospondylus (OWEN, 1865) WATSON, 1911
Etymology:
= Plesiosaurus homalospondylus OWEN, 1865

Holotype: BMNH 36184
Note: BENTON & SPENCER have YORYM G 502 as type.

Locality: Whitby, Yorkshire County, England, Southern United Kingdom.

Horizon:

Biostratigraphy: Hildoceras bifrons zone.

Age: Lower Toarcian Stage, Upper Lias Epoch, Early Jurassic.

Material: Vertebrae.

Referred material:

BMNH 40118, R1334, R1366-7, MM L7077, WM 854, YM502:

Vertebrae.

Philosophical Society of York: Skull and skeleton missing the distal end of paddles.

Trustees of the British Museum: Skull and skeleton.

 

HUENE & MAUBEUGE, 1952

Locality: Jeandelaincourt, Meurthe-et-Moselle Department, France.

Horizon:

Biostratigraphy:

Age: Lias Epoch, Early Jurassic.

Material:

Number: Not given: Cervical vertebrae.

 

PERSSON

Locality: Jeandelaincourt, Meurthe-et-Moselle Department, France.

Horizon:

Biostratigraphy: Aulacostephanus pseudomutabilis zone.

Age: Middle Lias Epoch, Middle Early Jurassic.

Material:

Number: Not given: Vertebrae.

 

= Plesiosaurus coelospondylus CONYBEARE, 1842
Etymology:

Holotype:

Locality: England, Southern United Kingdom.

Horizon: Liassic.

Biostratigraphy:

Age: Lias Epoch, Early Jurassic.

Material: Vertebrae.

Referred material:

Number: Not given: Vertebrae.

 

= Plesiosaurus latispinnus BENNEDEN, 1882 non OWEN, 1854
Etymology:

Holotype:

Locality: Dampicourt, Luxembourg.

Horizon:

Biostratigraphy:

Age: Middle Lias Epoch, Middle Early Jurassic.

Material: Vertebrae, pectoral and limb bones.

 

= Plesiosaurus brachypterygius HUENE, 1923
Etymology: Greek, brachys, "short" and Greek, pterygium, "wing-like."
= Microcleidus brachypterygius (HUENE, 1923), BAKKER, 1993
= Hydrorion brachypterygius (HUENE, 1923) GROßMANN, 2007

Holotype: GPIT/477/1/1

Locality: Quarry (Steinbuch) 29, Ohmden near Holzmaden, Baden-Wurttemberg State, Southern Germany.

Horizon: Posidonienschiefer.

Biostratigraphy: Lias epsilon II, 4 (unterer Schiefer), Harpoceras falcifer zone.

Age: Lower Toarcian Stage, Upper Lias Epoch, Late Early Jurassic.

Material: Skull and skeleton.

Referred material:

SMNS 51143: A nearly complete specimen in lateral view, only the anterior part of the skull is preserved.

SMNS 51141: A nearly complete juvenile specimen.

MH Nr 8: A nearly complete specimen.

Note: Lias E, uppemost ii, diretly below II2

= Plesiosaurus tournemirensis SCIAU, CROCHET & MATTEI, 1990
Etymology: In reference to the Village of Tournemire, Aveyron Department, South France.
= Occitanosaurus tournemirensis (SCIAU, CROCHET & MATTEI, 1990) BARDET, GODEFROIT & SCIAU, 1999

Holotype: Musee Municipal de la ville de Millau, Aveyron, MMM J. T. 86-100

Locality: Village of Tournemire, 43°56’25”N, 3°1’14”E, Aveyron Department, South France.

Horizon: Marnes feuilletees, Aalensis zone, Pleydellia celtica Subzone.

Biostratigraphy:

Age: Upper Toarcien Stage, Upper Malm Epoch, Early Jurassic.

Material: Skull and fragmentary skeleton.

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Species: macropterus (SEELEY, 1865) KUHN, 1934
= Plesiosaurus macropterus SEELEY, 1865
Etymology:

Holotype: SMC J35182

Locality: Loftus Alum Quarry, Loftus, Yorkshire County, England, Southern United Kingdom.

Horizon:

Biostratigraphy:

Age: Lias Epoch, Early Jurassic.

Material: Fragmentary skeleton.
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Species: melusinae VINCENT, WEIS, KRONZ & DELSTE, 2017
Etymology: French, melusine, the name of a mythical woman who is a serpent or fish from the waist down. Melusine is part of European folklore and is said to have been married to Count Siegfried, considered the first count of Luxenburg.

Holotype: MNHNL TV 424

Locality: Sanem, Esch-sur-Alzette canton, southwest of Luxembourg.

Horizon:

Biostratigraphy: Couches a Harpoceras flaciferum, Serpentinum Chronozone, Exaratum Subchronozon.

Age: Lower Toarcian Stage, Lower Lias Epoch, Early Jurassic.

Material: A skull wiht a patial postcranial skeleton.