Fossil of Cryptolithus tessellatus, from Dry Dredgers.

Belongs within: Asaphida.

The Trinucleidae were an Ordovician family of trilobites characterised by the presence of a broad marginal fringe around the head, covered in funnel-shaped, presumably sensory, pits. The posterior corners of the head bore often long and slender spines.

Characters (from Harrington et al. 1959): Cephalic fringe broad, sloping outward, bilaminar, with numerous opposed pits on external surfaces, extending posterolaterally somewhat behind rest of cephalon; convex occipital ring commonly with backward-directed spine, occipital furrow with deep apodermal pit; glabella expanding forward, reaching to inner margin of fringe, deep anterior pits at extremities of axial furrows; genae subtriangular in outline, with or without eye tubercles and faint eye ridges; lower lamellae of fringe bearing genal spines. Thorax with six segments; convex axial rings, with deep apodemal pits in articulating furrows; pleurae with broad diagonal pleural furrows, pleural tips bent down. Pygidium triangular, length 0.25 to 0.5 of width; axis with many rings; pleural fields with shallow pleural furrows. Surface of glabella and genae may bear reticulate pattern of raised ridges, margin of fringe and pygidial border with terraced lines.

| i. s.: Myttonia fearnsidesi Whittington 1966RC93
| Anebolithus simplicior (Whittard 1966)RC93
|--HanchungolithusRC93 [HanchungolithinaeB-HIO02]
| |--TrinucleusH04
| | |--T. concentricusW77
| | `--T. goldfussiH04
| `--Yinpanolithus Lu in Lu & Chang 1974B-HIO02
| |--*Y. yinpanensis Lu in Lu & Chang 1974B-HIO02
| |--Y. guizhouensis Yin in Yin & Li 1978B-HIO02
| |--Y. tenuilimbatus (Zhang in Qui et al. 1983)B-HIO02
| `--Y. wutangensis (Lu in Wang et al. 1962)B-HIO02
| |--C. portageeinsis Lespérance 1988RC93
| `--C. tesselatusP98
|--Salterolithus Bancroft 1929 [incl. Smeathenia Dean 1960]B-HIO02
| |--*S. caractaci (Murchison 1839) (see below for synonymy)B-HIO02
| `--S. harnagensis (see below for synonymy)B-HIO02
`--Broeggerolithus Lamont 1935 (see below for synonymy)B-HIO02
|--*B. broeggeri (Bancroft 1929) [=Cryptolithus broeggeri, *Broeggeria broeggeri]B-HIO02
| |--B. b. broeggeri [incl. B. constrictus Bancroft in Dean 1960]B-HIO02
| |--B. b. globiceps (Bancroft 1929) [=Cryptolithus globiceps, B. nicholsoni globiceps]B-HIO02
| |--B. b. soudleyensis (Bancroft 1929) [=Cryptolithus soudleyensis]B-HIO02
| `--B. b. ulrichi (Bancroft 1949) [=Salterolithus (Ulricholithus) ulrichi]B-HIO02
`--+--B. discors (Angelin 1854) [=Trinucleus discors, Cryptolithus dicors (l. c.)]B-HIO02
|--B. nicholsoni (Reed 1910) (see below for synonymy)B-HIO02
`--B. transiens (Bancroft 1929) [=Cryptolithus transiens, Broeggeria transiens]B-HIO02

Broeggerolithus Lamont 1935 [=Broeggeria Bancroft 1933 non Walcott 1902; incl. Ulricholithus Bancroft 1933 (n. n.)]B-HIO02

Broeggerolithus nicholsoni (Reed 1910) [=Trinucleus nicholsoni; incl. Cryptolithus longiceps Bancroft 1929, Broeggerolithus nicholsoni longiceps, B. melmerbiensis Dean 1962, B. simplex Dean 1960]B-HIO02

Salterolithus caractaci (Murchison 1839) [=Trinucleus caractaci; incl. T. intermedius Wade 1911, Salterolithus intermedius]B-HIO02

Salterolithus harnagensis Bancroft 1929 [=Broeggerolithus harnagensis; incl. Salterolithus caractaci var. paucus Cave 1957, Sa. praecursor Dean 1960, Sa. smeathenensis Bancroft in Dean 1958, Smeathenia smeathenensis]B-HIO02

*Type species of generic name indicated


[B-HIO02] Bowdler-Hicks, A., J. K. Ingham & A. W. Owen. 2002. The taxonomy and stratigraphical significance of the Anglo-Welsh Cryptolithinae (Trinucleidae, Trilobita). Palaeontology 45 (6): 1075–1106.

[H04] Haeckel, E. 1899–1904. Kunstformen der Natur. Bibliographisches Institut: Leipzig und Wien.

Harrington, H. J., G. Henningsmoen et al. 1959. Systematic descriptions. In Treatise on Invertebrate Paleontology pt O. Arthropoda 1 pp. O170–O540. Geological Society of America and University of Kansas Press.

[P98] Prothero, D. R. 1998. Bringing Fossils to Life: An introduction to paleobiology. WCB McGraw-Hill: Boston.

[RC93] Romano, M., W. T. Chang, W. T. Dean, G. D. Edgecombe, R. A. Fortey, D. J. Holloway, P. D. Lane, A. W. Owen, R. M. Owens, A. R. Palmer, A. W. A. Rushton, J. H. Shergold, D. J. Siveter & M. A. Whyte. 1993. Arthropoda (Trilobita). In: Benton, M. J. (ed.) The Fossil Record 2 pp. 279–296. Chapman & Hall: London.

[W77] White, C. A. 1877. Report upon the invertebrate fossils collected in portions of Nevada, Utah, Colorado, New Mexico, and Arizona, by parties of the expeditions of 1871, 1872, 1873, and 1874. U.S. Geographical Surveys West of the One Hundredth Meridian 4 (1): 1–219, pls 1–21.

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