Trimerus (Trimerus) harrisoni ( McCoy, 1876 )

Sandford, Andrew C., 2005, Homalonotid trilobites from the Silurian and Lower Devonian of south-eastern Australia and New Zealand (Arthropoda: Trilobita: Homalonotidae), Memoirs of Museum Victoria 62 (1), pp. 1-66 : 34-35

Trimerus (Trimerus) harrisoni ( McCoy, 1876)

Homalonotus harrisoni McCoy, 1876: 19 , pl. 23 fig. 11.

Trimerus harrisoni .— Gill, 1949: 65, text-fig. 1A.— Sandford, 2000: 189, figs. 17A–E.

Remarks. I recently provided a comprehensive synonymy, revised diagnosis and description for Trimerus (Trimerus) harrisoni (see Sandford, 2000). No new material has been obtained. Poor preservation of all known cranidia obscures many features of the cephalon pertinent to its subgeneric assignment. The glabella is not strongly raised, although this is true also of the type species Trimerus (Trimerus) delphinocephalus . The glabella tapers very strongly forwards, although whether bell shaped or trapezoid in outline is not clear as the best-preserved specimen is somewhat crushed. The poorly known pygidia of harrisoni resemble those of the type species in the depth and relative depth of the pleural and ring furrows, although differ in having a prominent postaxial ridge and possibly in lacking a posterior spine. In respect to these latter differences, the pygidial morphology of harrisoni is not incompatible with T. (Ramiotis). However, the strong tapering of the glabella and exceptional length of the preglabellar field are emphasised here in assigning the species to T. ( Trimerus ).