Saturday, January 16, 2021

Cambrian Trilobite Olenellus From Boston Area


In August 1900,  Amadeus W. Grabau (1870-1946) published Palaeontology of the Cambrian Terranes of the Boston Basin. He described an Olenellus (Burr, 1900) trilobite cephalon fossil on page 665 and shown on plate 34 figure 1a. 

Dr. Grabau writes "Among the material collected by Mr. H. T. Burr at North Weymouth are two very perfect heads of a species of Olenellus which appears to be undescribed... The larger head (Pl.34, fig. 1 a) (as compressed upon the slate) describes almost a semicircle in outline, with the centre at the base of the glabella. Width of head, 47 mm. Length at the centre, 24 mm. The postero-lateral angles project about 4 mm. behind the base of the occipital ring.

The glabella has the form of a n acute triangle, the anterior end forming the bluntly rounded apex of the triangle. The length of glabella is 20 mm., and the width of the occipital ring, 12.5 mm. There are three pairs of glabellar furrows in front of the occipital furrow. the latter is strongly marked for about a third of the distance inward, form the margin of the glabella on each side, and is continued across by a faint depression. It appears more like a pair of glabellar furrows, which are deep and rather wide at the margin, becoming shallower as they pass inward and gently backward... Eye lobes crescentric, relatively narrow."

"No specific name is present proposed for this species which is undoubtedly new, since the material is insufficient to establish a complete specific diagnosis. It probably belongs to a new subgenus of Olenellus." It was found "in the dark purplish Lower Cambrian slates of Pearl Street, Norht Weymouth," Massachusetts.

Figure was drawn by Miss Elvira Wood (1865-1928), Instructor in Paleontology in the Massachusetts Institute of Technology. She drew a large number of  images for this document. On page 694, Dr. Grabau writes "To Miss Elvira Wood and Miss L.R. Martin thanks are due for the care and labor bestowed on the illustrations of the fossils."