Fossil of Cryptolithus tessellatus, from Dry Dredgers.

Belongs within: Trilobita.

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.

<==Trinucleidae [Trinucleina]
    |--Marrolithinae B-HIO02
    |--Hanchungolithinae B-HIO02
    |--Yinpanolithus Lu in Lu & Chang 1974 [Trinucleinae] B-HIO02
    |    |--*Y. yinpanensis Lu in Lu & Chang 1974 B-HIO02
    |    |--Y. guizhouensis Yin in Yin & Li 1978 B-HIO02
    |    |--Y. tenuilimbatus (Zhang in Qui et al. 1983) B-HIO02
    |    `--Y. wutangensis (Lu in Wang et al. 1962) B-HIO02
    `--Cryptolithinae B-HIO02
         |--Cryptolithoides B-HIO02
         |--Cryptolithus tesselatus P98
         |--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 (preoc.); 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.

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.

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