Alternative spelling: Librostoma
Full reference: R. A. Fortey. 1990. Ontogeny, hypostome attachment and trilobite classification. Palaeontology 33(3):529-576
Parent taxon: Trilobita according to M. C. Ebach and K. J. McNamara 2002
See also Fortey 1990 and Hughes 1994
Sister taxa: Aglagalia, Agraulaeva, Aguaraya, Aldonaiidae, Altajaharpes, Amechilus, Amgaspididae, Ampellatocephalina, Anacopodia, Antagmidae, Antatlaeva, Atopidae, Auritamidae, Avoninidae, Batchatiella, Bathynotidae, Beikedamaspis, Bergerolimbus, Burlingiidae, Carmon, Changshaniidae, Chinensis, Corynexochida, Crossoura, Curiaspis, Cuyanaspis, Cyclolenzellina, Dalmanites troosti, Deltacare, Devonocoryphe, Edganocare, Elleria, Elleria morani, Ellipsocephaloididae, Ellipsuella, Entomostracites, Erbenochile, Eulomella, Eutrilobita, Fabulaspis, Faciura, Gentilaspis, Gigmpeltis, Goycoia, Harpetida, Helioproetoides, Holocephalinidae, Howelluella, Idiorapha, Ignotogregatidae, Indigestus, Irvingelloides, Ishpella, Isocolidae, Issafenia, Ityophoridae, Jamrogiidae, Jonotus, Juriietella, Kamlacus, Kanfuqingia, Leptopilus, Lichida, Llanoaspididae, Loxopeltis, Lusampa, Mapaniidae, Megalaspidicus, Meneghinella, Metapopristis, Monkaspididae, Moolatrilo, Moretaeva, Moretarva, Namanoiidae, Neochilonorria, Neomalungia, Neotaenicephalus, Nepeidae, Odontopleurida, Ogygiocaridinae, Olenida, Onchonotopsidae, Opisthoparia, Orictocara, Otekmaspis, Otenaspella, Paichiashania, Paleoaethia, Parakingaspidoides, Pararania, Peculicephalina, Perissopyge, Phacopida, Piliolites, Pliomerellus, Poculicephalina, Polycyrtaspididae, Prodamesella, Proetida, Proparia, Pseudoacicaudus, Pseudoclelandia, Pseudocrecephalaspina, Pseudosalteria, Pseudosarkia, Pseudotermierella, Ptyttstrigis, Punctaspis, Redlichiida, Remopleuridacea, Repinaella, Resseria, Resseropsis, Rochaeva, Sarkiidae, Serksia, Serksioides, Sibiriopeltis, Sphaerocare, Spizharaspis, Stittaspis, Sukhanaspis, Sunaspididae, Taidonurus, Taplimella, Tazemmourtia, Thymurus, Toxotis, Trapezocephalina, Triarthrella, Trilobus, Tuberaspis, Tuyunaspis, Ulrickaspis, Utiidae, Westergardia, Winsteria, Wuaniidae, Zigzuella
Subtaxa: Asaphida Ptychopariida Trinucleida
Distribution:
• Silurian of Algeria (1 collection), Australia (1), Austria (1), Canada (3: Northwest Territories, Quebec), the Czech Republic (5), Italy (2), Morocco (2), the United Kingdom (4), United States (2: Arkansas, Georgia)
• Dobrotivian of the Czech Republic (4), France (8), Morocco (2), Portugal (3), Spain (11)
• Uhaku of Belarus (2), Latvia (1), Lithuania (2), Norway (24), the Russian Federation (3), Sweden (15)
• Liben of the Czech Republic (1)
• Letna of the Czech Republic (2)
• Chazyan of Canada (33: Newfoundland and Labrador, Northwest Territories, Ontario, Quebec), United States (64: California, New York, Oklahoma, Tennessee, Vermont)
• Whiterockian of Canada (55: Newfoundland, Newfoundland and Labrador, Northwest Territories, Quebec), China (6), Norway (4), United States (89: California, Nevada, New York, Oklahoma, Utah, Vermont)
• Fennian of France (1), United States (1: Nevada)
• Volkhov of Argentina (1), Estonia (2), Latvia (2), Lithuania (4), Norway (1), the Russian Federation (39), Sweden (52)
• Hunderum of Sweden (14)
• Langevoja of Sweden (27)
• Valaste of Sweden (11)
• Dawan of China (8)
• Klabava of the Czech Republic (2), France (2)
• Arenig of Argentina (13), Australia (29), Bolivia (11), Canada (3: Newfoundland and Labrador), China (126), France (6), Greenland (1), Iran (1), Morocco (3), Norway (5), the Russian Federation (2), Spain (1), Sweden (8), the United Kingdom (8), United States (8: Montana, Nevada, New York, North Dakota, Vermont)
• Arenigian of Argentina (54), Canada (2: Northwest Territories), China (43), the Russian Federation (1), United States (7: Nevada, Utah)
• Ordovician to Silurian of Canada (2: Québec)
• Ordovician of Argentina (110), Australia (79), Belarus (4), Belgium (4), Bolivia (6), Canada (201: Alberta, British Columbia, Manitoba, Newfoundland, Newfoundland and Labrador, Northwest Territories, Northwest Terrorities, Nunavut, Nunvait, Ontario, Quebec, Québec, Yukon), China (291), the Czech Republic (27), Estonia (20), Finland (1), France (14), Greenland (4), Iran (17), Ireland (29), Italy (3), Kazakhstan (11), Kyrgyzstan (2), Latvia (4), Lithuania (12), Morocco (30), the Netherlands (1), New Zealand (1), North Korea (1), Norway (333), Oman (2), Peru (3), Poland (2), Portugal (6), the Russian Federation (76), Saudi Arabia (1), South Korea (4), Spain (22), Sweden (229), Turkey (5), the United Kingdom (277), United States (1283: Alaska, British Columbia, California, Georgia, Idaho, Illinois, Illinois, Iowa, Indiana, Iowa, Iowa/Wisconsin, Kentucky, Maine, Maryland, Michigan, Minnesota, Missouri, Montana, Nevada, New Mexico, New York, North Dakota, Ohio, Oklahoma, Pennsylvania, Pennsylvania and Virginia, Tennessee, Texas, Utah, Virginia, Wisconsin, Wyoming), Venezuela (1), Vietnam (1)
• Canadian of Canada (3: Newfoundland, Newfoundland and Labrador, Northwest Territories), United States (3: Maryland, Utah)
• Cressagian of South Korea (1), the United Kingdom (3)
• Tremadoc of Antarctica (1), Argentina (164), Bolivia (7), Canada (90: Alberta, Newfoundland and Labrador, Northwest Territories, Yukon), China (102), Colombia (2), the Czech Republic (3), France (7), Iran (13), Mexico (22), Morocco (2), Norway (2), the Russian Federation (14), Spain (3), Sweden (3), the United Kingdom (1), United States (7: Montana, Texas, Utah, Vermont, Virginia)
• Ibexian of Norway (4), United States (13: California, Nevada)
• Skullrockian of Argentina (1), Canada (26: Alberta, British Columbia, Newfoundland), Greenland (1), United States (41: Nevada, New York, Texas, Utah)
• Taoyuanian of China (62), the Russian Federation (25), South Korea (59), Turkey (2)
• Amgan of the Czech Republic (3), Iran (1), Kazakhstan (4), Norway (1), the Russian Federation (3), United States (3: Alaska, Utah)
• Solvan of Canada (41: British Columbia, Newfoundland and Labrador), the Czech Republic (7), Greenland (1), Kazakhstan (1), the Russian Federation (1), Spain (1), United States (92: Nevada, Pennsylvania)
• Delamaran of Canada (41: Alberta, British Columbia, New Brunswick, Northwest Territories), Mexico (3), Morocco (4), United States (203: California, California-Nevada, Idaho, Montana, Nevada, Nevada and California, Pennsylvania, Utah, Vermont, Virginia)
• Ordian of Australia (1)
• Cambrian to Ordovician of Canada (1: Quebec), the Russian Federation (2)
• Waucoban of Canada (1: British Columbia), Greenland (1)
• Cambrian of Antarctica (8), Argentina (13), Australia (95), Canada (222: Alberta, Alberta-British Columbia, Brithish Columbia, British Columbia, New Brunswick, Newfoundland, Newfoundland and Labrador, Northwest Territories, Nunavut, Quebec, Yukon, Yukon Territory), China (531), the Czech Republic (14), Denmark (1), France (8), Germany (22), Greenland (26), India (34), Iran (7), Italy (1), Kazakhstan (146), Kyrgyzstan (1), Morocco (2), North Korea (1), Norway (7), Poland (2), the Russian Federation (107), South Korea (22), Spain (18), Sweden (1), Turkey (28), the United Kingdom (14), United States (846: Alabama, Alaska, Arizona, Arkansas, California, Colorado, Georgia, Idaho, Idaho/ Utah, Indiana, Massachusetts, Minnesota, Missouri, Montana, Nevada, Nevada and Utah, New Mexico, New York, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Wisconsin, Wyoming, Wyoming-Montana), Vietnam (1)
• Caerfai of United States (1: New York)
Total: 7250 collections including 16469 occurrences